THE  DECENNIAL  PUBLICATIONS  OF 
THE  UNIVERSITY  OF  CHICAGO 


PHYSICAL  CHEMISTRY  IN  THE  SERVICE 
OF  THE  SCIENCES 


VAN  T  HOFF 


THE  DECENNIAL  PUBLICATIONS  OF 
THE  UNIVERSITY  OF  CHICAGO 


THE  DECENNIAL  PUBLICATIONS 


ISSUED  IN  COMMEMORATION  OP  THE  COMPLETION  OP  THE   FIRST  TEN 
YEARS  OP  THE  UNIVERSITY'S   EXISTENCE 


AUTHORIZED  BY  THE  BOARD  OP  TRUSTEES  ON  THE  RECOMMENDATION 
OF  THE    PRESIDENT  AND  SENATE 


EDITED  BY   A  COMMITTEE  APPOINTED  BY  THE  SENATE 

EDWARD  CAPPS 

STARR  WILLABD  CUTTING  ROLLIN  D.  SALISBURY 

JAMES  ROWLAND  ANGELL,      WILLIAM  I.  THOMAS  SHAILER  MATHEWS 

CARL  DARLING  BUCK  FREDERIC  IVES  CARPENTER         OSEAR  BOLZA 

JULIUS  STIEGLITZ  JACQUES  LOEB 


THESE  VOLUMES  ARE  DEDICATED 

TO  THE  MEN  AND  WOMEN 

OF  OUR  TIME  AND  COUNTRY  WHO  BY  WISE  AND  GENEROUS   GIVING 

HAVE  ENCOURAGED  THE  SEARCH  AFTER  TRUTH 

IN  ALL  DEPARTMENTS   OF   KNOWLEDGE 


CROCKER 


PHYSICAL  CHEMISTRY  IN  THE  SERVICE 

OF  THE  SCIENCES 


PHYSICAL  CHEMISTRY  IN  THE 
SERVICE  OF  THE  SCIENCES 


BY 

JACOBUS  H.  VAN  'T  HOFF 

MEMBER  OF  THE  PRUSSIAN  ACADEMY  OF  SCIENCES,  PROFESSOR  ORDINARIES   HONORARIUS  IN 

THE  UNIVERSITY  OF  BERLIN,   SPECIAL    LECTURER  AT  THE  DECENNIAL 

CELEBRATION  OF  THE  UNIVERSITY  OF  CHICAGO 


ENGLISH  VERSION  BY 

ALEXANDER  SMITH 

OF  THE  DEPARTMENT  OF  CHEMISTRY 


THE  DECENNIAL  PUBLICATIONS 
SECOND  SERIES    VOLUME  XVIII 


CHICAGO 

THE  UNIVERSITY  OF  CHICAGO  PRESS 
1903 


Copyright  1903 

BY  THE  UNIVERSITY  OF  CHICAGO 


HERRN  DR.  WILLIAM  RAINEY  HARPER, 

PBESIDENTEN  DER  UNIVERSITAT  CHICAGO, 

der  mit  einem  Organisations-Talent,  das  mich  mit  Bewunderung 
erftillt,  innerhalb  zehn  Jahre  eine  grosse  Universitat  ins  Leben 
gerufen  hat,  mochte  ich  diese  englische  Ausgabe  meines  Werkes 
widmen.  Dass  unter  seiner  Ftihrerschaft  der  Einfluss,  welchen 
sich  die  junge  Anstalt  schon  zu  verschaffen  gewusst  hat,  von  Jahr 
zu  Jahr  an  Ausdehnung  und  Tiefe  gewinnen  moge,  ist  mein 
aufrichtiger  Wunsch. 

J.  H.  VAN  'T  HOFF. 
CHARLOTTENBURG, 

16ten  Juni,  1903. 


125517 


AUTHOR'S  PREFACE 

THE  following  lectures,  delivered  June  20-24,  1901,  were 
given  at  the  invitation  of  the  University  of  Chicago  on  the 
occasion  of  the  decennium  of  its  foundation.  The  time  for 
preparation  being  limited,  the  lectures  were  given  extempore 
and  the  version  here  presented  was  adapted  for  publication 
from  the  stenographic  report.  In  order  that  the  whole  may 
present  as  far  as  possible  a  memorial  of  the  interesting  fest- 
ival, the  changes  made  have  been  confined  within  the  nar- 
rowest possible  limits.  The  introductory  lecture,  which 
appears  in  this  volume  as  the  first  lecture  of  the  series,  was 
delivered  as  one  of  the  addresses  before  a  general  educa- 
tional conference,  held  in  the  lecture  theater  of  the  Kent 
Chemical  Laboratory,  to  which  the  guests  of  the  University 
were  invited. 

CHARLOTTENBURG, 
January,  1902. 


PKEFACE  TO  THE  ENGLISH  VERSION 

DURING  the  festivities  in  connection  with  the  celebration 
of  the  decennium  of  its  foundation,  the  University  of  Chi- 
cago was  honored  by  the  presence  of  a  number  of  the  mosl. 
distinguished  scientific  men  of  the  world.  Among  these, 
Professor  van  't  Hoff,  who  received  the  honorary  degree  oil 
LL.D.,  was  one  of  the  most  prominent. 

As  this  volume  is  in  some  degree  a  memorial  of  Professor 
van  't  Hoff's  visit,  no  apology  need  be  offered  for  printing 
here  the  words  pronounced  by  the  President  of  the  Univer- 
sity when,  at  the  convocation  ceremony  of  Tuesday,  June  18, 
1901,  the  honorary  degree  was  conferred: 

JACOB  HENRY  VAN  'T  HOFF, 

Professor  of  Physical  Chemistry  in  the  University  of 
Berlin;  investigator  who  has  brought  to  bear  upon 
chemical  problems  a  keen  and  logical  mind;  endowed 
with  speculative  and  imaginative  powers  of  the  highest 
order;  founder  of  the  theory  explaining  the  space  rela- 
tions of  atoms  in  molecules — a  theory  which  is  essen- 
tial to  a  comprehension  of  the  chemistry  of  organized 
„  and  inorganized  matter ;  master  in  the  field  of  dynamic 
chemistry;  investigator  and  brilliant  discoverer  in  the 
domain  of  the  modern  theory  of  solutions — a  theory 
which  constitutes  one  of  the  greatest  advances  made 
by  chemical  science  in  the  last  quarter  of  a  century: 
for  these  splendid  and  fertile  achievements,  by  the 

xiii 


xiv  PHYSICAL  CHEMISTRY 

authority  of  the  Board  of  Trustees  of  the  University  of 
Chicago,  upon  nomination  of  the  University  Senate,  I 
confer  upon  you  the  degree  of  Doctor  of  Laws  of  this 
University,  with  all  the  rights  and  privileges  appertain- 
ing thereunto. 

Professor  van  't  Hoff  most  cordially  consented,  not  only 
thus  to  visit  the  United  States  as  one  of  the  guests  of  the 
University,  but  also,  at  the  special  request  of  the  Department 
of  Chemistry,  to  deliver  a  course  of  lectures  on  that  branch  of 
chemistry  which  owes  so  large  a  share  of  its  recent  develop- 
ment to  his  brilliant  and  profound  investigations. 

The  lectures  were  delivered  in  English,  and,  in  slightly 
condensed  form,  are  reproduced  in  this  volume.  The  interest 
which  they  aroused  was  most  gratifying  both  to  the  lecturer 
and  to  his  hosts.  They  were  attended  by  large  audiences, 
which  included  professors  of  chemistry  and  related  sciences 
from  many  distant  states  of  the  Union.  Those  who  had  the 
privilege  of  hearing  them  will  not  soon  forget  the  genial 
personality  of  the  speaker,  the  simple  and  lucid  language, 
and  the  suggestive  treatment  which  combined  to  make  them 
memorable. 

The  excellent  portrait,  a  reproduction  of  which  forms  the 
frontispiece,  will  give  added  interest  to  the  book. 

The  plate  showing  a  sheet  of  tin  attacked  by  the  "tin- 
disease"  was  made  from  a  photograph  kindly  furnished  by 
Dr.  Ernst  Cohen. 

ALEXANDER  SMITH. 

CHICAGO,  AUGUST,  1902. 


TABLE  OF  CONTENTS 
INTRODUCTORY 

PAGE 

LECTURE  I  3 

Kekule*'s  View,    that   Thirty    Years   Ago    Chemistry   Had 
Reached   a   Dead   Point — Structural    Chemistry  Leads   to 
Stereochemistry — The  New  Physical  Chemistry — The  Genius 
of  Physical  Chemistry  Exhibited  by  Discussion  of  Osmotic    ' 
Pressure — Calculation  of  Osmotic  Pressure  from  Temperature  | 
and    Concentration — Applications    of    the    Conception    of 
Osmotic  Pressure  in  Biology — Loeb's  Fertilization  Experi- 
ment. 

PHYSICAL  CHEMISTRY  AND  PURE  CHEMISTRY 

LECTURE  II  15 

Plan  of  the  Lectures — Modern  Physical  Chemistry  Distin- 
guished from  the  Earlier  Physical  Chemistry,  and  its  Nature 
Defined — It  Rests  on  Two  Foundations:  the  Extension  of 
Avogadro's  Law  to  Solutions,  and  Thermodynamics — The 
Extension  of  Avogadro's  Law — The  Thermodynamical  Prin- 
ciple of  the  Conservation  of  Energy — The  Thermodynamical 
Principle  of  Carnot-Clausius — Reversible  Cycles — Illustra- 
tions of  the  Application  of  These  Principles — The  First  Great 
Service  of  Physical  Chemistry  in  the  Field  of  Pure  Chem- 
istry— Application  of  a  New  and  Comprehensive  Principle  for 
the  Study  of  Inorganic  Problems — Case  of  Carnallite  as 
Illustration — Graphic  Representation  of  the  Results. 

LECTURE  III  -      31 

The  Second  Great  Achievement  of  Physical  Chemistry  in  the 
Field  of  Pure  Chemistry — Berthelot's  Principle  of  Maximum 
Work— Many  Facts  Contradict  It— The  New  Conception 
that  Change  Occurs  Only  When  Work  Can  Be  Done— The 

xv 


xvi  PHYSICAL  CHEMISTRY 

PAGE 

Methods  of  Determining  Which  Changes  Will  Be  Able  to 
Do  Work— The  Thermochemical  Method— The  Electrical 
Method — The  Third  Great  Achievement  of  Physical  Chem- 
istry in  the  Field  of  Pure  Chemistry— The  Theory  of  loniza- 
tion — Qualitative  and  Quantitative  Illustrations  of  the  Use 
of  This  Theory. 

PHYSICAL  CHEMISTRY  AND  INDUSTRIAL  CHEMISTRY 
LECTURE  IV     -  45 

The  Co-operation  of  Physical  and  Industrial  Chemistry — 
Two  Illustrations  to  Be  Discussed— Results  of  Scientific 
Study  of  Carnallite  and  Possibilities  of  Their  Commercial 
Application  to  the  Manufacture  of  Potassium  Chloride — The 
Recent  Discoveries  in  Connection  with  Alloys  and  Steel, 
Introduced  by  a  Description  of  the  Peculiar  Behavior  of  Tin, 
and  its  Explanation — White  and  Gray  Tin  and  Their  'Transi- 
tion Point  at  20° — The  Methods  of  Determining  the  Transi- 
tion Point — Use  of  the  Dilatometer — The  Electrical  Method. 

LECTURE  V       -  58 

Results  of  the  Physico-Chemical  Study  of  Wrought  Iron,  Cast 
Iron,  and  Steel — Complications  Introduced  by  the  Presence 
of  Carbon  and  the  Occurrence  of  Solid  Solutions — Method  of 
Studying  Iron  by  Polishing,  Etching,  and  the  Use  of  the 
Microscope — Constituents  are  Ferrite,  or  Pure  Iron;  Marten- 
site,  or  the  Solid  Solution  of  Carbon  in  Iron;  Cementite,  or 
the  Carbide  of  Iron;  Graphite,  or  Free  Carbon;  Pearlite,  or  the 
Cryohydratic  Mass — Two  Forms  of  Ferrite  with  Transi- 
tion Point  at  850° — Pearlite,  a  Mixture  of  Cementite  and  Fer- 
rite, and  its  Formation  and  Composition — Hard  Steel  is 
Overcooled  Martensite — The  Graphite — The  Behavior  of 
Melted  Iron  Rich  in  Carbon — Rapid  Cooling  Gives  White 
Cast  Iron  Containing  Much  Cementite — Slow  Cooling  Gives 
Gray  Cast  Iron  by  Decomposition  of  the  Cementite  and  Pro- 
duction of  Graphite,  and  Finally  Pearlite — A  Numerical  Illus- 
tration of  the  Behavior  of  Molten  Iron  Containing  6%  per 
Cent,  of  Carbon  When  Cooled  (1)  Rapidly  and  (2)  Slowly. 


1 


TABLE  OF  CONTENTS  xvii 


PHYSICAL  CHEMISTRY  AND  PHYSIOLOGY 

PAGE 

LECTURE  VI  -      73 

,*, 

The  Theory  of  Solutions  Based  upon  the  Extension  of  Avo- 

gadro's  Principle  and  its  Importance  in  Physiology — Osmotic    • 
Pressure  and  Osmotic  Phenomena — The  Experiments  of  de 
Vries  with  Plant  Cells— The  Work  of  Donders  and  Ham-  • 
burger  with  Blood  Corpuscles — The  Experiment  of  Massart 
with  the  Human  Eye  and  with  Bacteria — Loeb's  Work  on 
Artificial  Fertilization — The  Measurement  of  Osmotic  Pres-   • 
sure — Observation  of  the  Freezing  Points  for  Determining 
Equality  of  Osmotic  Pressure — Specific  Action  of  Ions  in    ? 
Physiology. 

LECTURE  VII  -      84 

Enzymes,  Their  Preparation  and  Nature — Enzymes  as  Cat- 
alytic Agents — Chemical  Equilibrium — Graphic  Representa- 
tion of  Incomplete  Chemical  Interactions — Incomplete  Actions 
Occur  When  the  Heat  Change  is  Small — Application  to  the 
Behavior  of  Enzymes — Illustrations — The  Synthesis  of 
Amygdalin. 


PHYSICAL  CHEMISTRY  AND  GEOLOGY 

LECTURE  VIII  -      97 

The  Formation  and  Structure  of  Geological  Salt  Deposits — 
Early  Study  of  Deposition  from  Solutions  Containing  Several 
Salts,  by  Usiglio — The  Proportion  of  the  Constituents  as 
Well  as  Their  Solubility  to  Be  Considered— The  Modern 
Method  of  Study  and  Graphic  Representation — The  Case  of 
a  Single  Salt  and  Water  at  a  Fixed  Temperature,  25°— The 
Case  of  Two  Salts  Simultaneously  Present  at  25°— The  Case 
of  Three  Salts  at  25°— The  Problem  of  Sea-Water  at  25°, 
with  All  Salts  Present. 


xviii  PHYSICAL  CHEMISTRY 

PAGE 

LECTURE  IX  115 

The  Influence  of  Time  and  of  Variations  in  Temperature  and 
Pressure  on  Deposition — The  Time  Factor  and  Delayed 
Crystallization — Several  Compounds,  Found  in  Nature,  Do 
Not  Appear  at  All  in  Laboratory  Experiments  on  Deposition, 
But  Can  Be  Included  in  the  Scheme  by  the  New  Method  of 
Agitation  with  Solutions — The  Behavior  at  Temperatures 
above  25° — New  Minerals  Formed  above  25°  and  Absent  at 
25° — New  Combinations  of  Minerals  Possible  above  25° — 
Disappearance  above  25°  of  Minerals  Formed  at  That  Tem- 
perature— The  Influence  of  Possible  Changes  in  Pressure  is 
Too  Slight  to  Affect  the  Results. 

INDEX 125 


INTRODUCTORY 


'v        •      ".  /'„'       ' 

J  J  '  J   J   <  >  J 

: 


' 


LECTUKE  I 

INTRODUCTORY 

Kekule"'s  View,  that  Thirty  Years  Ago  Chemistry  Had  Reached  a  Dead 
Point — Structural  Chemistry  Leads  to  Stereochemistry — The 
New  Physical  Chemistry — The  Genius  of  Physical  Chemistry 
Exhibited  by  Discussion  of  Osmotic  Pressure  —  Calculation  of 
Osmotic  Pressure  from  Temperature  and  Concentration — Applica- 
tions of  the  Conception  of  Osmotic  Pressure  in  Biology — Loeb's 
Fertilization  Experiment. 

INASMUCH  as  during  the  next  few  days  I  am  to  deliver  a 
number  of  lectures  on  certain  topics  of  a  physico-chemical 
nature,  I  should  like  to  throw  my  address  before  this  educa- 
tional conference  into  the  form  of  an  introduction  to  these 
lectures. 

I  must  begin  by  saying  at  the  outset  that  one  of  our  best 
modern  historians  of  the  science  of  chemistry,  Ladenburg,1 
expresses  the  opinion  that  the  most  characteristic  feature  of 
the  chemistry  of  the  last  fifteen  or  twenty  years  is  the  contin- 
ued increase  in  the  prominence  of  this  physical,  or,  as  many 
say,  general,  chemistry.  Will  you  allow  me,  therefore,  briefly 
to  explain  how  this  physical  chemistry  has  been  developed, 
and  what  its  present  importance  is,  and  will  you  permit  me 
in  doing  so  to  refer  to  personal  recollections  to  some  extent  ? 

Thirty  years  ago,  when,  as  a  young  student  in  the 
University  of  Bonn,  I  first  became  acquainted  with  the  sci- 
ence of  chemistry,  under  the  instruction  of  one  of  the  most 

l  Entwickelung  der  Chemie  in  den  letzten  20  Jahren,  Stuttgart,  1900. 

3 


PHYSICAL  CHEMISTKY 


noted  of  chemists,  Kekule",  that  science  was  pronounced  by 
our  master  to  have  reached  a  dead  point,  and  to  be  without 
visible  prospect  of  new  advance. 

At  that  time  the  belief  in  the  existence  of  atoms,  although 
only  an  indirect  conclusion  from  chemical  facts,  seemed 
to  be  well-founded.  The  molecular  theory,  which  had  been 
chiefly  developed  in  connection  with  physics,  lent  strong 
support  to  it.  The  details  in  regard  to  the  relations  of  the 
atoms  in  the  molecule  were  known,  or  at  all  events  the 
attainment  of  this  knowledge  in  the  case  of  the  more  com- 
plex or  newer  substances  was  only  a  question  of  time.  Thus, 
the  formula  of  methyl  alcohol  was: 

H\ 

H— C - O - H 

H/ 

This  expressed  the  fact  that  in  a  molecule  of  this  substance, 
four  hydrogen  atoms,  each  represented  by  the  letter  H, 
along  with  one  atom  of  carbon  and  one  of  oxygen,  repre- 
sented respectively  by  the  letters  C  and  O,  were  present, 
and  that  they  were  attached  to  one  another  in  the  manner 
shown  by  the  connecting  lines. 

Realistic  as  this  conception  was,  it  was  very  clearly 
recognized  that  such  symbols  were  but  mental  pictures  or 
diagrams  on  paper,  and  chemistry  was  looking  for  some 
Newton  who  should  discover  the  laws  according  to  which 
the  atoms  themselves  were  held  together  in  their  molecular 
configuration  to  form  one  complete  whole. 

As  we  probably  are  all  aware,  however,  no  Newton  of 
this  kind  arrived,  and  yet  only  a  few  years  after  Kekul6's 


INTRODUCTORY 


unfortunate  utterance  (a  sort  of  remark,  we  may  say  in 
passing,  such  as  a  teacher  ought  perhaps  never  to  make 
before  his  pupils)  there  arose  the  conceptions  of  stereo- 
chemistry, giving  birth  to  a  new,  but  now  well-developed 
and  vigorous,  branch  of  our  science. 

By  means  of  stereochemistry  so  much  at.  least  was 
accomplished  that,  the  real  existence  of  the  atoms  being 
assumed,  not  only  was  their  mode  of  union  described  but 
also  their  relative  positions  in  the  molecule  was  determined. 
The  above  symbol  for  methyl  alcohol  now  became  a  tri- 
dimensional  model,  with  the  carbon  in  the  center  of  a  tetra- 
hedron, at  whose  four  equidistant  points  the  three  hydrogen 
atoms  and  the  hydroxyl  group  were  situated. 

We  remained,  however,  and  after  twenty-five  years  still 
remain,  unacquainted  with  the  laws  which  control  these 
relative  positions.  Perhaps,  by  the  help  of  the  new  con- 
ception of  electrons,  we  may  be  on  the  eve  of  getting  a 
clearer  knowledge  of  the  condition  of  the  atoms,  at  least 
in  the  neighborhood  of  the  absolute  zero  of  temperature. 

During  these  twenty-five  years,  however,  investigation 
still  proceeded,  although  in  an  entirely  different  direction. 
It  did  not  advance  by  the  elaboration  of  symbol  archi- 
tecture, with  atoms  as  the  bricks.  About  fifteen  years  after 
Kekule"'s  unfortunate  expression,  a  second  child  of  hope,  the 
new  physical  chemistry,  came  into  being.  It  did  not  arise 
all  at  once :  there  is  hardly  a  branch  of  science  in  which  this 
occurs.  It  was  developed  like  a  small  plant,  unseen  in  the 
shade;  at  length  it  feels  the  sun  and  promises  to  expand 
into  a  colossal  tree. 


6  PHYSICAL  CHEMISTRY 

Some,  like  Duhem,1  go  so  far  as  to  claim  for  physical 
chemistry  the  rank  of  a  third  science,  and  range  it  beside 
the  sciences  of  physics  and  chemistry.  Others,  like  Winkler2 
and  Ladenburg,  favor  the  view  that  a  prominent  place  within 
the  territory  of  chemistry  should  be  devoted  to  physical 
chemistry,  and  that  the  previous  subdivision  into  organic 
and  inorganic  should  be  replaced  by  a  division  into  three. 
In  this  connection,  it  is  of  interest  to  mention  that  at  the 
present  moment  the  University  of  Gottingen  is  planning  to 
organize  its  chemical  department  on  this  basis. 

Leaving  aside  all  principles  of  subdivision,  which  must 
always  be  of  an  arbitrary  nature,  since  science,  like  that 
nature  which  it  reflects,  must  be  one  great  whole,  I  should 
like  here  to  answer  the  question,  What  has  this  physical 
chemistry  brought  to  pass? 

This  question  may  be  taken  in  either  one  of  two  ways, 
general  and  particular,  and  answered  accordingly.  One 
might,  on  the  one  hand,  exhibit  the  general  conclusions,  and, 
taking  this  sense,  I  should  have  to  speak  of  the  laws  of 
chemical  change,  of  reaction  speed,  and  of  electrochemical 
processes.  Yet  even  so  I  should  be  unable  to  do  this 
without  using  complicated  formulae,  which  the  character  of 
this  introduction  forbids. 

On  the  other  hand,  the  genius  of  physical  chemistry  may 
be  portrayed  by  a  study  of  one  of  the  special  problems 
which  it  has  been  in  a  position  to  solve.  It  is  in  this  direc- 


1"  Une  science  nouvelle :  La  chimie  physique,"  Revue  philomat ique  de  Bordeaux 
etdu  Sud-Ouest,  1899. 

ZBerichte  d.  deutsch.  chem.  Gesell.,  Vol.  XXXIV,  p.  399. 


INTRODUCTORY 


tion  that  I  prefer  to  proceed  in  answering  the  above  ques- 
tion, and  I  shall  ask  your  attention  to  one  of  the  best  known 
and  most  far-reaching  achievements  of  physical  chemistry. 
It  is  connected  with  the  establishment  and  application  of 
the  conception  of  osmotic  pressure. 

By  way  of  approaching  this  special  problem,  consider  the 
attraction  for  water  shown  by  some  well-known  substances, 
like  quicklime.  If  a  bottle  is  filled  up  with  this  and  is 
loosely  stoppered,  the  lime  will  attract  water  from  the  moist 
air,  will  swell  up,  and,  finally,  no  matter  how  strong  the 
bottle  may  be,  will  inevitably  break  the  vessel  which  con- 
tains it.  An  enormous  force  is  developed  by  this  attraction 
for  water,  so  great  that  it  has  not  been  found  pos'sible 
to  subject  the  pressure  to  exact  measurement. 

A  similar  but  less  violent  phenomenon  can  be  observed, 
and  may  be  measured,  provided  we  confine  ourselves  to 
dilute  solutions.  Thus,  sugar,  even  in  dilute  solution,  shows 
this  attraction  for  water  to  a  marked  degree.  We  take,  fol- 
lowing Pfeffer,1  a  one  per  cent,  solution  of  sugar,  and  fill  with 
it  a  vessel  whose  walls  are  porous,  so  as  to  permit  the  pas- 
sage of  the  water  alone.  A  suitably  prepared  battery  jar 
will  serve  the  purpose.  We  place  this,  after  closing  it,  in 
pure  water,  and  find  that  the  latter,  attracted  by  the  sugar 
solution,  forces  its  way  through  the  porous  wall  until  at  7°, 
if  the  vessel  is  sufficiently  strong  to  withstand  it,  a  pressure 
of  two-thirds  of  an  atmosphere  is  attained.  This  sort  of 
pressure  is  called  osmotic  pressure. 

We  can  now  proceed  further  to  generalize,  and  say  that 

l  Oamotische  Untersuchungen,  Leipzig,  1877. 


8  PHYSICAL  CHEMISTRY 

J  every  substance  capable  of  dissolving  will  attract  the  solvent. 
This  is,  in  fact,  only  another  way  of  referring  to  the  ten- 
dency to  dissolve.  Conversely,  the  solid  substance  is  in 
turn  attracted  by  the  solvent,  and  diffuses  into  it  when  it  is 
furnished  an  opportunity  to  do  so.  In  the  latter  case  the 
osmotic  pressure  appears  in  another  light,  and  becomes  the 
pressure  which  prevents  the  undissolved  molecules  from 
freely  moving  into  the  surrounding  solvent,  when  a  state  of 
saturation  has  been  reached.  After  the  same  fashion,  gas 
molecules  exercise  gaseous  pressure  in  the  direction  of 
an  empty  space  when  they  are  hindered  by  a  partition  from 
entering  it. 

This  osmotic  pressure  was  studied  as  early  as  a  hundred 
years  ago,  •  especially  with  reference  to  its  significance  in 
physiological  processes.  It  was  found  to  have  a  definite 
value.  This  seemed,  at  first,  to  be  dependent  upon  the 
nature  of  the  membrane,  to  vary  with  the  nature  of  the 
dissolved  substance  and  of  the  solvent,  to  be  obviously 
dependent  upon  the  concentration,  and  likewise  to  be  very 
sensitive  to  change  of  temperature.  These  were  essentially 
the  facts  known  about  osmotic  pressure  up  to  the  time  at 
which  the  path  being  blazed  by  physical  chemistry  encoun- 
tered it. 

The  result  was  unexpectedly  simple.  So  plain  was  it 
that  now  one  can  even  calculate  the  osmotic  pressure  (for  a 
dilute  solution  of  a  non-electrolyte)  when  the  concentration 
and  temperature  are  given.  The  whole  relation  is,  in  fact, 
presented  in  the  expression 


INTRODUCTORY  9 


in  which  P  is  the  osmotic  pressure  in  atmospheres,  T  the 
absolute  temperature,  and  C  the  concentration  or  the  num- 
ber of  gram- molecules  of  the  dissolved  body  per  liter  of 
solution.  The  numerical  value  of  Pfeffer's  observation  upon 

the  one  percent,  solution  of  sugar,  in  which  T==  273°  -f  7°  or 

•        10 
280°    and    C  =  oTn  >  is    obtained  at  once   from  the  above 

formula. 

I  should  like  to  emphasize  the  differences  in  the  methods 
of  physical  chemistry  and  its  manner  of  procedure  when 
compared  with  those  of  stereochemistry.  The  former  does 
not  primarily  seek  the  solution  of  its  problems  in  any  con- 
ception of  the  nature  of  matter.  The  above  formula  contains, 
so  far  as  this  is  concerned,  only  the  relative  molecular 
weight,  which,  where  investigation  in  the  form  of  a  gas  is 
possible,  corresponds  to  the  gas  density.  Physical  chemis- 
try therefore  confines  itself  to  numerical  relations  between 
directly  measurable  magnitudes. 

In  spite  of  the  limitation  which  physical  chemistry  thus 
imposes  upon  itself,  it  is  certainly  a  strong  evidence  of  its 
sound  foundation  and  healthy  power  to  develop  that  it  shows 
itself,  in  a  continually  increasing  degree,  capable  of  solving 
those  problems  which,  on  account  of  their  direct  relation  to 
life,  seem  to  be  the  most  complex.  If  we  take  into  con- 
sideration the  colossal  labors  which  were  spent  in  the  service 
of  atomic  conceptions,  it  must  be  admitted  that  relatively 
little  has  been  accomplished  by  them  in  this  particular 
direction.  The  very  opposite  can  be  stated  of  the  labors  of 
the  physical  chemist.  As  long  as  ten  years  ago,  in  Utrecht,1 

luOver  de  physiologische  beteekenis  der  jongste  stroomingen  op  chemisch 
physisch  gebied,"  Natuur-  en  Geneeskundig  Congres,  Utrecht,  1891. 


10  PHYSICAL  CHEMISTRY 

I  employed  an  opportunity  like  the  present  to  refer  to  the 
tremendous  r6le  which  osmotic  pressure,  whose  laws  have 
been  laid  bare  by  physical  chemistry,  plays  in  many  of  the 
processes  of  living  organisms. 

At  that  time  I  was  able  to  present  the  results  of  several 
physiological  investigations,  which  tended  to  show  that 
osmotic  pressure  is  a  fundamental  factor  in  the  most  various 
life-functions  of  animals  and  plants.  According  to  de  Yries ' 
it  regulates  the  growth  of  plants.  According  to  Bonders  and 
Hamburger 2  it  regulates  the  functions  of  the  red  blood  cor- 
puscles, and  thus  of  the  blood.  According  to  Massart3  it  con- 
trols some  of  the  functions  of  the  human  eye,  as  well  as  the 
life  of  the  seeds  of  disease,  and  deadly  organisms  like  the 
bacilli  of  typhoid  fever. 

Since  that  time  the  literature  of  this  subject  has  grown 
until  it  would  easily  fill  a  large  and  comprehensive  volume.4 
Perhaps  the  most  pregnant  fact  of  all  is  that  which  has 
been  established  in  this  very  University  of  Chicago  by  Loeb. 
It  is  to  the  effect  that  the  act  of  fertilization  of  lower  ani- 
mals, like  sea-urchins,  can  be  in  part  replaced  by  a  definite 
increase  in  the  osmotic  pressure  of  the  liquid  in  which  the 
unfertilized  egg  is  lying.  The  development  starts  and  even 

i u  Eine  Methods  zur  Analyse  der  Turgorkraft,"  Pringsheims  Jahrbucher,  Vol. 
XIV. 

2  Onderzoekingen  gedaan  in  het  physiologisch  Laboratorium  der  Utrechtsche 
Hoogeschool,  (3),  Vol.  IX,  p.  26. 

3  Extrait  des  archives  de  biologie,  Liege,  1889. 

*  A  compilation  extending  to  1900  is  given  by  KOEPPE,  Physikalische  Chemie  in 
der  Medizin,  Wien,  1900.  See  also  the  very  full  bibliography  in  BURTON  E.  LIVING- 
STON'S Rdle  of  Diffusion  and  Osmostic  Pressure  in  Plants,  University  of  Chicago 
Press,  1903. 


INTRODUCTORY  11 


proceeds  to  the  production  of  a  motile  organism.  I  may 
most  fitly  conclude  in  the  words  with  which  the  investiga- 
tor just  named  closed  an  address1  given  on  the  present  subject : 
"At  no  time  since  the  period  immediately  following  the  dis- 
covery of  the  law  of  conservation  of  energy  has  the  outlook 
for  the  progress  of  physiology  appeared  brighter  than  at 
present,  this  largely  being  due  to  the  application  of  physical 
chemistry  to  the  problems  of  life." 

1"  The  Physiological  Problems  of  Today,"  American  Society  of  Naturalists, 
Ithaca,  1897. 


PHYSICAL  CHEMISTRY  AND  PURE    CHEMISTRY 


LECTURE  II 

PHYSICAL  CHEMISTRY  AND  PURE  CHEMISTRY 

Plan  of  the  Lectures — Modern  Physical  Chemistry  Distinguished  from 
the  Earlier  Physical  Chemistry,  and  its  Nature  Defined  —  It  Rests 
on  Two  Foundations,  the  Extension  of  Avogadro's  Law  to  Solutions 
and  Thermodynamics — The  Extension  of  Avogadro's  Law — The 
Thermodynamical  Principle  of  the  Conservation  of  Energy — The 
Thermodynamical  Principle  of  Carnot-Clausius — Reversible  Cycles 
— Illustrations  of  the  Application  of  These  Principles — The  First 
Great  Service  of  Physical  Chemistry  in  the  Field  of  Pure  Chemis- 
try— Application  of  a  New  and  Comprehensive  Principle  for  the 
Study  of  Inorganic  Problems — Case  of  Carnallite  as  Illustration 
—  Graphic  Representation  of  the  Results. 

I  WILL  begin  by  setting  before  you  the  scheme  of  that 
which  I  desire  to  develop  in  these  lectures.  I  have  divided 
the  material  into  four  parts,  each  of  which  refers  to  physical 
chemistry,  but  gives  a  view  from  a  different  standpoint. 
The  object  of  this  is  to  show  the  relations  to,  and  the 
influence  upon,  different  branches  of  science,  pure  or  applied, 
which  physical  chemistry  is  able  to  exhibit. 

I  should  wish  to  consider  physical  chemistry,  in  the  first 
place,  in  its  application  to  pure  chemistry,  and,  in  the  second 
place,  in  its  relation  to  applied  or  technical  chemistry.  Then 
I  shall  devote  two  lectures  to  the  relation  of  physical  chem- 
istry to  physiology,  since  the  characteristic  of  the  develop- 
ment of  physiology  in  recent  years  seems  to  lie  in  the  fact 
that  it  has  made  application  of  physico-chemical  methods. 

15 


16  PHYSICAL  CHEMISTRY 

Finally,  I  should  like  to  show  by  a  few  examples  how  physi- 
cal chemistry  attempts  to  attack  geological  problems. 

Beginning  with  the  relation  between  physical  chemistry 
and  pure  chemistry,  I  must  first  briefly  delimit  that  which  at 
the  present  day  we  understand  by  the  former  title.  If  we 
take  the  expression  in  its  most  general  sense,  it  refers  evi- 
dently to  the  application  of  physical  expedients,  methods,  and 
instrument's  to  chemical  problems.  Interpreted  in  this  way, 
one  might  state  that  when  Lavoisier  made  chemistry  the 
science  which  it  is,  he  simultaneously  founded  physical 
chemistry.  He  did  this  inasmuch  as  he  applied  the  balance, 
obviously  a  physical  instrument,  to  the  testing  and  establish- 
ing of  fundamental  laws  in  the  realm  of  chemistry.  Later, 
when  Bunsen,  in  his  universally-known  investigations  with 
the  spectroscope,  determined  the  composition  of  the  sun  and 
stars,  it  could  be  said  with  equal  right  that  physical  chemis- 
try was  involved,  since  the  spectroscope  is  classed  as  a 
piece  of  physical  apparatus.  In  this  way  ever  greater 
advances  in  our  science  have  been  bound  up  with  the  intro- 
duction of  physical  methods  of  observation  and  measure- 
ment. 

Apart  from  this,  it  is  said,  and  said  correctly,  that  physi- 
cal chemistry  is  a  recent  development  of  the  last  fifteen 
years.1  I  should  like  to  explain  in  what  way  this  last  phase 
in  its  development  may  be  considered  as  having  especially 
profound  significance.  The  introduction  of  the  spectroscope 
by  Bunsen,  and  the  later  employment  of  the  calorimeter  in 

i  NEBNST,  Address  at  the  Opening  of  the  Institute  of  Physical  Chemistry  and 
Electro-chemistry,  GOttingen,  1896. 


PURE  CHEMISTRY  17 


the  chemical  laboratory  by  Berthelot  and  Thomson,  were  of 
the  highest  importance,  but  were  limited  to  a  particular  mani- 
festation, such  as  the  emission  of  light  or  the  production  of 
heat.  Now,  what  physical  chemistry  in  the  latest  period  has 
done,  or  has  claimed  to  do,  did  not  consist  in  the  introduction 
of  new  apparatus  or  of  a  new  method  of  observation.  The 
most  recent  development  of  physical  chemistry  has  been  char- 
acterized rather  by  the  establishment  of  comprehensive  prin- 
ciples which  fertilize  the  whole  foundation  of  the  science,  and 
promise  to  furnish  nourishment  for  a  large  part  of  the  chem- 
istry of  the  future.  I  should  be  glad  if  I  could  exhibit  one 
of  these  fundamental  principles  in  application  before  you  in 
the  same  manner  as  a  lecture-experiment  is  shown.  Yet  this 
practical  procedure  is  precisely  that  which  the  character  of 
the  new  development  expressly  excludes,  since  it  has  not 
brought  into  use  essentially  new  apparatus  and  methods, 
but  rather  new  laws,  which  are  unfortunately  not  of  the  sim- 
plest description. 

I  remember  very  well  that  as  a  student  I  was  never  able 
to  understand  the  real  import  of  Avogadro's  law,  and  that  I 
received  the  first  glimpse  of  its  bearing  when  I  explained  it 
in  teaching  and  applied  it  in  experiment.  And  yet  the  prin- 
ciples which  I  have  to  lay  before  you  are  still  further 
removed  by  their  abstract  character  from  the  range  of  every- 
day thought  than  even  the  law  of  Avogadro.  If,  therefore, 
I  were  to  attempt  to  build  up  these  principles  from  their 
foundations,  those  to  whom  they  were  new  would  probably 
find  their  time  had  been  wasted,  since  they  would  have  no 
opportunity  for  gaining  a  correct  understanding  of  them  by 


18 


PHYSICAL  CHEMISTRY 


FIG.  i 


actual  application.  On  the  other  hand,  those  to  whom  these 
principles  are  already  known  might  justly  complain  that 
nothing  new  had  been  set  before  them. 

Thus  I  have  considered  it  most  advisable  not  to  enter 
upon  the  study  of  these  principles  very 
deeply,  but  to  -assume  them  as  known. 
I  shall  prefer  to  take  for  detailed  consid- 
eration the  application  of  these  principles 
to  the  answering  of  definite  questions, 
and  thus,  so  far  as  possible,  to  break  new 
ground. 

There  are  in  the  main  two  foundations 
on  which  the  recent  development  of  physical  chemistry 
rests:  the  extension  of  the  law  of  Avogadro  and  thermody- 
namics. The  particular  extension  of  Avogadro's  law  referred 
to  may  easily  be  connected  with  the  con- 
tent of  the  original  rule  when  the  latter  is 
expressed  in  the  following  form:  If  we 
take  a  fixed  volume  (Fig.  1)  of  any  gas, 
for  example,  oxygen,  then  we  know  that 
it  exercises  a  pressure  upon  the  walls  of 
the  vessel.  This  pressure,  probably  pro- 
duced by  the  impact  of  the  molecules, 
may  be  measured  by  a  manometer  such  as  that  shown  in  the 
figure.  Its  value  depends  upon  the  temperature  and  we  may 
assume  this  to  be  recorded  by  the  thermometer  and  to  be, 
for  example,  20°.  Now,  Avogadro's  rule  states  that  if  into 
an  equal  space  (Fig.  2)  we  introduce  so  much  of  another 
gas,  for  example  carbon  dioxide,  that  at  the  same  tempera- 


FIG.  2 


PURE  CHEMISTRY  19 


ture  (20°)  an  equal  pressure  is  exercised,  then  both  spaces 
must  contain  equal  numbers  of  molecules  of  their  respective 
gases.  We  might  consider  this  number  to  be  1000  in  each 
case.  The  absolute  number  is  unknown  and  only  the  equality 
in  the  number  is  postulated. 

The  expansion  of  this  principle  is  concerned  with  solu- 
tions. In  these  also  an  effect  comparable  with  gaseous 
pressure  is  exercised.  The  gaseous  pressure  has  to  do  with 
the  fact  that  a  gas  endeavors  to  diffuse  into  a  vacant  space 
and  thus  presses  upon  the  impermeable  walls,  which  prevent 
its  further  progress.  In  the  same  way,  in  a  solution,  also,  the 
dissolved  substances  tend  to  diffuse  into  the  pure  solvent 
when  the  solution  and  solvent  are  in  contact.  This  may  be 
seen  when  the  liquids  are  carefully  placed  one  above  the 
other  in  the  same  vessel  in  such  a  way  that  that  which  is 
specifically  lighter  is  placed  upon  the  top.  A  partition, 
impermeable  by  the  dissolved  body,  which  did  not  interfere 
with  contact  between  the  solution  and  the  solvent  (which,  in 
other  words,  was  permeable  by  the  solvent),  would  restrain 
this  diffusion  and  experience  a  pressure.  This  pressure  is 
obviously  the  so-called  osmotic  pressure  which  has  already 
been  mentioned  (p.  7)  in  the  introduction.  The  extension 
of  Avogadro's  principle  consists  in  this:  that  for  a  given  sub- 
stance the  osmotic  pressure  is  equal  in  value  to  the  gaseous 
pressure,  provided  the  temperatures  and  the  concentrations, 
that  is,  the  quantities  in  unit  volume,  are  the  same.  From 
this  it  follows  immediately  that  two  solutions  of  different  bod- 
ies containing  equal  numbers  of  molecules  in  equal  volumes, 
provided  they  are  at  the  same  temperature,  exercise  the 


20  PHYSICAL  CHEMISTRY 

same  osmotic  pressure.  Not  only  so,  but  when  the  molecular 
weight  is  known,  this  pressure,  like  the  gaseous  pressure, 
can  be  calculated  with  ease.  For  our  purpose,  it  is  unneces- 
sary to  pursue  this  law  by  further  numerical  illustration. 
We  shall  add  only  that  this  law  of  Avogadro  and  its 
extension  (and  be  it  remarked,  the  extension  is  a  most  com- 
prehensive one,  since  it  applies  to  all  soluble  bodies  and  to 
all  solvents)  is  restricted  in  its  application  within  certain 
limits.  It  claims  strict  accuracy,  both  in  the  original  and 
extended  forms,  only  when  the  dilution  is  very  great,  or,  in 
other  words,  only  under  conditions  which  cannot  be  realized 
practically.  Nevertheless,  at  dilutions  which  correspond  to 
that  of  atmospheric  air,  that  is  to  say,  in  the  case  of  gases  at 
a  pressure  of  one  atmosphere  and  in  the  case  of  solutions  of 
an  analogous  concentration  (about  one-tenth  normal),  the 
deviations,  in  most  cases  where  the  principles  find  applica- 
tion, are  insignificant. 

So  much  for  the  first  principle  which  has  contributed  to 
the  recent  development  of  physical  chemistry,  and  is  often 
named  the  theory  of  solutions.  The  second  concerns  the 
application  of  thermodynamics,  and  particularly  of  the  law 
of  conservation  of  work  or  energy,  and  of  the  Carnot-Clausius 
principle  to  chemical  questions.  What  I  said  in  the  begin- 
ning about  Avogadro's  law,  to  the  effect  that  the  correct 
appreciation  of  its  content  can  be  reached  by  most  students 
only  after  application  to  definite  problems  encountered  in 
independent  research,  might  be  said  perhaps  with  even 
greater  truth  of  the  principle  which  is  now  to  be  discussed. 

The  principle  of  the  conservation  of  energy  is  in  itself 


PURE  CHEMISTRY  21 


simple  enough.  No  energy  arises  or  disappears.  Change 
in  form  in  an  unchanging  amount  is  alone  possible.  The 
forms  with  which  we  have  to  do  in  the  treatment  of  chemical 
problems  are  in  the  main  mechanical  work,  heat,  light,  and 
electrical  energy.  The  whole  preliminary  knowledge  required 
consists  in  knowing  that  when  mechanical  work  is  converted 
into  heat  425  kilogram-meters  give  exactly  one  calorie ;  when 
electric  energy  is  turned  into  heat,  one  gram-equivalent  at 
a  tension  of  one  volt  gives  23  calories. 

The  Carnot-Clausius  principle  is  far  from  simple.  This 
conception,  again,  I  never  understood  until  I  had  occasion 
to  apply  it  in  my  investigations,  and  to  test  it  in  numerical 
calculations.  While  Avogadro's  law  can  be  stated  in  few 
words,  this  is  impossible  in  the  present  case.  Further,  the 
principle  of  Carnot-Clausius  finds  expression  in  so  many 
different  forms  that  even  after  practice  it  is  not  very  easy  to 
handle.  Since  it  is  possible  that  among  the  younger 
students  of  science  present  there  may  still  be  some  who  have 
yet  to  take  their  first  step  into  this  region  by  applying  its 
conceptions  to  chemical  problems,  I  shall  make  a  suggestion 
as  to  the  choice  of  the  most  suitable  form  of  this  principle. 
It  may  be  applied  by  carrying  out  so-called  reversible  cycles 
of  operations  or  by  the  introduction  of  abstract  physical 
conceptions  and  mathematical  functions,  such  as  entropy,  as 
is  done  by  physicists  like  Gibbs,  Planck,  and  Duhem.  I  am 
convinced  that,  for  the  chemist,  the  first  form,  in  which 
reversible  cycles  are  employed,  is  the  most  advantageous. 
The  difficulty  that  is  then  encountered  is  confined  to  the 
conception  of  a  "reversible  cycle." 


22  PHYSICAL  CHEMISTRY 

Briefly  stated,  a  cycle  consists  in  a  series  of  changes  in 
course  of  which  the  original  condition  is  reached.  Thus, 
for  example,  we  permit  ice  to  evaporate,  condense  the  vapor 
to  water,  and  then  freeze  the  water.  These  changes  are 
reversible,  provided  they  take  place  under  such  conditions 
that  the  change  can  proceed  in  either  direction.  This  is 
true,  for  example,  when  water  is  frozen  in  a  region  where 
the  temperature  is  0°  C.,  and  where,  therefore,  ice  can  just 
as  well  melt.  At  temperatures  above  or  below  0°  only  one 
or  other  of  these  processes  can  take  place.  Now,  in  such  a 
cycle  of  operations  —  and  this  is  the  content  of  the  Carnot- 
Clausius  principle  —  the  sum  of  the  quantities  of  heat  (§), 
divided  by  the  absolute  temperature  (T)  at  which  it  is  com- 
municated, is  equal  to  zero. 


A  very  simple  application  which  frequently  throws  an 
unexpected  light  on  chemical  problems  is  to  be  noted  when 
the  reversible  cycle  is  carried  out  at  constant  temperature. 
Here  the  equation  obviously  becomes: 


That  is  to  say,  the  sum  of  the  heats  communicated  is  equal 
to  zero,  or,  in  other  words,  no  heat  passes  into  any  other  form 
of  energy,  such  as,  for  example,  mechanical  work.  The 
sum  of  the  work  (A)  accomplished  in  the  course  of  the 
operations  is,  therefore,  likewise  zero. 


PURE  CHEMISTRY  23 

Applying  this,  for  instance,  to  the  above  cycle  with  ice- 
water  and  vapor,  we  draw  at  once  the  important  conclusion 
that  at  0°  the  vapor  tension  of  water  and  ice  must  be  equal. 
Considering  processes  more  closely  allied  to  chemistry — such 
as  the  reversible  change  of  rhombic  and  monoclinic  sulphur 
at  96°,  and  that  of  cyamelid  and  cyanuric  acid  at  150° — we 
infer  that  there  must  be  equality  in  each  case  between  the 
vapor  tensions  of  the  two  forms  of  sulphur,  and  between  the 
so-called  dissociation  pressures  of  cyamelid  and  cyanuric 
acid  at  the  point  of  change  into  gaseous  cyanic  acid.  In 
the  latter  case  we  encounter  another  great  advantage  in  the 
application  of  the  Carnot-Clausius  principle.  This  is  that 
the  complexity  of  the  nature  of  the  process  under  considera- 
tion does  not  introduce  the  slightest  difficulty.  The  com- 
position of  the  bodies,  for  example,  is  of  so  little  importance 
that  atomic  and  molecular  conceptions  need  not  be  consid- 
ered, and,  strictly  speaking,  in  the  last-mentioned  case,  it 
need  only  be  known  that  cyanuric  acid,  cyamelid,  and  cyanic 
acid  have  the  same  percentage  composition,  since  otherwise 
the  cycle  of  operations  could  not  be  carried  out. 

I  must  limit  myself  to  the  foregoing  brief  remarks  on  the 
principles  of  Avogadro  and  Carnot-Clausius,  and  proceed  to 
lay  before  you  what  is  attainable  by  their  application.  In 
doing  this  I  must  first  refer  to  those  who,  few  in  number 
and  not  always  working  under  the  most  favorable  conditions, 
during  the  last  fifteen  years  have  brought  physical  chemis- 
try to  its  present  state  of  development.  The  very  first  place 
must  be  given  to  Ostwald,  who  by  his  comprehensive  activity 
as  a  teacher,  his  astonishing  literary  labors,  and  his  powers 


24  PHYSICAL  CHEMISTRY 

of  organization  has  perhaps  done  more  than  any  other  for 
the  spread  of  physical  chemistry.  I  name  along  with  him 
Arrhenius,  whose  introduction  of  the  theory  of  electrolytic 
dissociation,  and  Nernst,  whose  application  of  the  same 
theory,  have  opened  up  an  entirely  unsuspected  field  in  the 
region  of  electric  phenomena. 

The  greatest  progress  is  promised  and  the  greatest  prog- 
ress has  been  achieved  by  the  application  of  physical  chem- 
istry to  that  part  of  the  science  which  is  usually  designated 
inorganic.  This  includes  all  the  elements  save  carbon, 
whose  chemistry,  as  you  know,  is  classed  as  organic.  That 
new  principles  ultimately  to  be  applied  to  the  whole  science 
are  more  easily  introduced  in  connection  with  the  former, 
depends  on  the  simpler  character  of  inorganic  problems. 
Inorganic  elements,  like  potassium  and  chlorine,  give  usually 
a  single  compound,  like  potassium  chloride.  When  the  ele- 
ment carbon  (C)  is  taken  into  consideration,  however,  this 
is  all  changed,  and  the  combination  of  this  element  with 
hydrogen  (H),  for  example,  offers  a  seemingly  innumerable 
number  of  possibilities,  such  as  CH4,  C2H4,  C2H2,  etc. 

Glancing  at  what  has  been  achieved  in  inorganic  chemis- 
try, three  advances  may  be  noted.  First,  it  may  be  said  that 
physical  chemistry,  in  the  handling  of  inorganic  problems, 
has  introduced  an  entirely  new  and  comprehensive  method 
of  work.  Secondly,  we  are  in  possession  of  a  principle 
which  enables  us  to  foretell  in  what  direction  and  how  far  a 
chemical  change  will  proceed.  Thirdly,  physical  chemistry 
has  thrown  new  light  on  the  nature  of  the  solutions  of  the 
so-called  electrolytes ;  that  is  to  say,  of  bases,  acids,  and  salts. 


PURE  CHEMISTRY  25 


I  hope  to  have  the  opportunity  of  illustrating  each  of 
these  three  achievements  by  describing  a  particular  case. 
In  order  first  to  bring  before  you  the  new  mode  of  treating 
inorganic  problems,  I  shall  describe  its  application  to  the 
study  of  carnallite,  a  mineral  of  technical  importance,  and 
known  to  be  a  compound  (double  salt)  of  magnesium  chlo- 
ride, potassium  chloride,  and  water.  Let  me  add  that  the 
investigation  in  question  was  carried  out  in  co-operation 
with  Meyerhoffer,  but  that  the  method  of  treating  inorganic 
compounds  which  is  illustrated  by  it  was  originally  developed 
more  particularly  by  Bakhuis-Roozeboom. 

If  you  look  up  the  subject  of  carnallite  in  the  earlier 
text-books  you  will  find  the  formula  MgCl2  .KC1 .6H2O, 
with  the  statement  that  the  compound  is  colorless  and  crys- 
talline, and  that  it  dissolves  in  water  easily,  with  separation 
of  potassium  chloride.  You  will  find  also  the  method  of 
preparation,  and  some  further  single,  disconnected  data. 
The  new  method  of  studying  the  subject  leads,  however,  to  a 
completely  exhaustive  knowledge  of  the  subject.  It  is 
based  essentially  on  a  better  comprehension  of  the  equilib- 
rium relationships  in  complex  chemical  phenomena,  and  of 
the  influences  which  temperature,  proportions  of  material, 
and  pressure  exercise  upon  them.  We  have,  for  example, 
discovered  so-called  transition  temperatures  in  complicated 
chemical  changes,  which  have  the  closest  resemblance  to 
simple  physical  melting-points.  Thus,  according  as  one 
passes  above  or  below  this  temperature,  a  complete  change 
in  one  direction  or  the  other  takes  place.  This  change  is, 
however,  of  a  complex  chemical  nature.  We  have  dis- 


26  PHYSICAL  CHEMISTRY 

covered  the  phase-rule  in  terms  of  which  the  most  dif- 
ferent sorts  of  equilibria  can  be  uniformly  interpreted. 
Finally,  we  have  made  easier,  and  in  some  cases  for 
the  first  time  made  possible,  the  achievement  of  a  know- 
ledge of  the  whole  circumstances  of  a  chemical  change 
in  relation  to  temperature  and  pressure,  by  an  extensive 
application  of  graphic  methods.  Carnallite  presents  an 
especially  good  example  of  the  last,  and  I  should  like  par- 
ticularly to  call  your  attention  to  the  fact  that  a  very  mini- 
mum of  observations  puts  us  in  possession  of  a  complete 
knowledge  of  its  whole  behavior. 

The  problem  before  us  is  this:  Carnallite  being  a  com- 
pound of  magnesium  and  potassium  chlorides  and  water, 
what  arises  when  these  three  substances  are  brought  together 
in  different  proportions,  at  different  temperatures,  and  the 
escape  of  the  water  is  prevented  ?  It  is  needless  to  add 
that  all  these  conditions  are  easily  realized  in  experimental 
work. 

In  considering  this  question  we  shall  start  from  the 
beautiful  transformation  which  carnallite  undergoes  in  pres- 
ence of  water  when  the  temperature  is  lowered. 

If  the  amount  of  water  added  is  not  too  great,  a  part  of 
the  carnallite  is  dissolved,  some  potassium  chloride  separates 
in  solid  form,  and  a  corresponding  excess  of  magnesium 
chloride  is  found  in  the  solution.  When  the  temperature  is 
now  lowered  the  dissolved  quantities  vary  on  account  of 
changes  in  solubility.  About  —21°,  however,  a  partial 
solidification  of  the  liquid,  akin  to  freezing,  begins.  This 
change  resembles  freezing  also,  in  the  fact  that,  in  spite  of 


PURE  CHEMISTRY  27 

continuous  removal  of  heat,  a  thermometer  shows  that  the 
temperature  remains  constant  at  —21°.  The  same  con- 
stancy is  observed  when  heat  is  added,  while  melting  of  a 
greater  or  less  proportion  of  the  solid  part  takes  place. 
Approaching  the  study  of  the  phenomenon  more  closely,  we 
find  that  the  carnallite  at  this  temperature  decomposes  as 
heat  is  removed,  and  that  water  is  taken  up,  according  to 
the  equation  : 

.  12H2O+KC1  . 


At  —21°  equilibrium  exists  between  these  two  conditions, 
just  as  at  0°  the  same  relation  subsists  between  water  and 
ice.  On  each  side  of  this  temperature  one  or  other  is  alone 
stable.  This  relationship  may  be  expressed  by  writing  the 
equation  in  the  form: 

MgCl2  .  KC1  .  6H20  +  6H20  ±?  MgCl2  .  12H2O  -f  KC1  . 

—  21° 

This  statement,  however,  does  not  include  all  the  facts  in 
regard  to  the  phenomenon,  since  the  water  in  contact  with 
the  carnallite  and  the  two  other  bodies  has  dissolved  some 
of  each  substance,  and  the  composition  of  this  solution  is 
expressed  by  the  formula  : 

[H20  +  0.066MgCl2  +  0.005KC1]. 

Thus  the  exact  equation  has  the  following  form: 

0.208(MgCl2  .  KC1  .  6H2O)  +  6[H2O  +  0.066MgCl2  +  0.005KC1] 
=  0.604(MgCla  .  12H20)  +  0.238KC1  . 

When  these  proportions  are   employed,   below   —21°  com- 


28  PHYSICAL  CHEMISTBY 

plete  solidification  takes  place,  while  above  it  only  potassium 
chloride  and  solution  remain. 

Viewing  the  system  in  relation  to  this  chemical  change, 
it  must  now  be  remarked  that  the  solution  which  is  there 
present,  and  whose  composition  has  just  been  given,  is  the 
starting  point  of  three  series  of  saturated  solutions  which 
are  obtained  by  changing  the  proportions  of  the  materials. 
If,  in  the  first  place,  we  take  somewhat  more  water,  then 
even  when  the  temperature  is  lowered  the  solution  remains. 
It  is  saturated  with  MgCl2 .  12H2O  and  potassium  chloride, 
and  has  a  definite  composition  peculiar  to  each  tempera- 
ture. We  shall  note  this  composition  only  at  the  point 
where  a  new  transformation  occurs.  This  is  at  —34°,  where 
ice  is  formed.  Here  everything  becomes  solid,  and  the 
liquid  disappears.  At  this  point  the  composition  of  the 

solution  is 

[H2O'+0.043MgCl2  +0.003KC1]  . 

If  we  now  follow  the  relations  at  higher  temperatures,  two 
limiting  cases  are  possible,  according  as  an  excess  of 
MgCl.  12H2O  or  of  KC1  is  present  along  with  the  carnal- 
lite.  In  the  former  case  we  encounter  at  —17°  the  melting 
point  of  MgCl2. 12H2O;  in  the  latter  at  168°  that  of  the 
carnallite. 

Time  does  not  permit  us  to  pursue  the  consideration  of 
the  subject  in  further  detail,  but  it  is  obvious  from  what  has 
been  said  that  the  conditions  for  the  formation  and  existence 
of  carnallite  can  be  gradually  delimited.  In  temperature 
they  must  lie  between  —21°  and  168°,  and  between  these 
points  the  solutions  from  which  carnallite  is  formed  may 


PURE  CHEMISTRY 


29 


have  a  maximum  content  either  of  magnesium  chloride  or 
potassium  chloride  up  to  saturation  with  either.  Thus  we 
find  a  region  in  which  its  existence  is  possible,  and  this 
region  is  capable  of  graphic  representation. 

Three  axes  are  obviously  required :  one  for  the  tempera- 


FIG.  3 


ture,  OX  (Fig.  3),  and  two  others  for  the  amounts  of  MgCl2 
and  KC1  in  the  saturated  solution,  which  are  designated  OY 
and  OZ  respectively.  It  is  the  composition  of  this  solution 
that  determines  the  nature  of  the  solid  bodies  which  will 
come  out.  Our  transition  temperature  and  the  correspond- 
ing composition  of  the  solution  are  represented  by  the  point 
E.  The  three  solubility  curves  proceeding  from  this  point 
are  ED,  terminating  in  the  freezing-point  of  the  solution  at 


30  PHYSICAL  CHEMISTRY 

D;  EF,  with  the  melting-point  of  MgCl2 . 12H2O  at  F;  EM, 
with  the  melting-point  of  carnallite  at  M.  The  whole  car- 
nallite  area  is  bounded  by  EFGHTKM.  Within  this  lie  all 
the  possible  methods  of  forming  it  by  employment  of  the 
simple  components ;  on  passing  outside  this  area  we  encounter 
all  the  possibilities  of  partial  or  complete  decomposition. 

The  rest  of  Fig.  3  has  been  obtained  by  the  addition  of 
data  of  a  simpler  kind  which  fit  into  the  scheme  as  follows : 
In  the  plane  XOZ  lies  the  solubility  curve  of  potassium 
chloride,  CP,  which  marks  the  limit  of  the  deposition  of 
potassium  chloride  from  pure  water.  Since  the  line  DEM 
corresponds  to  the  presence  of  the  maximum  amount  of  mag- 
nesium chloride,  a  potassium  chloride  area  arises  which  is 
limited  on  the  left  by  the  boundary  PCDEM.  Similarly,  a 
magnesium  chloride  area  fits  into  this,  complicated  by  the 
occurrence  of  various  hydrates,  which  is  bounded  on  the  left 
by  the  line  BFiFED.  An  ice  area  closes  the  whole  on  the 
left  and  connects  the  three  cryohydric  points,  B,  C,  and  D, 
with  A,  which  represents  the  freezing-point  of  pure  water. 


LECTURE  III 

PHYSICAL  CHEMISTRY  AND  PURE  CHEMISTRY 

The  Second  Great  Achievement  of  Physical  Chemistry  in  the  Field  of 
Pure  Chemistry— Berthelot's  Principle  of  Maximum  Work — Many 
Facts  Contradict  It  —  The  New  Conception  that  Change  Occurs 
Only  When  Work  Can  Be  Done— The  Methods  of  Determining 
Which  Changes  Will  Be  Able  to  Do  Work  — The  Thermochemical 
Method— The  Electrical  Method  — The  Third  Great  Achievement 
of  Physical  Chemistry  in  the  Field  of  Pure  Chemistry — The 
Theory  of  lonization  —  Qualitative  and  Quantitative  Illustrations 
of  the  Use  of  This  Theory. 

THE  second  service  of  physical  chemistry  to  pure  chem- 
istry depends  on  the  fact  that  it  has  established  the  funda- 
mental principle  which  enables  us  to  predict  from  other  data 
whether  a  given  chemical  change  will  take  place  or  not. 
When  this  chemical  change  is  one  which  reaches  a  condition 
of  equilibrium,  as  is  often  the  case,  then  the  principle  per- 
mits also  the  prediction  of  the  extent  to  which  the  change 
will  go. 

You  may  be  aware  that  a  principle  of  this  kind  was 
stated  by  Thomson  and  by  Berthelot,  and  received  from  the 
latter  the  name  of  principe  du  travail  maximum.  This 
principle  was  a  very  simple  one,  since  it  stated  merely  that 
the  heat  which  is  developed  by  a  chemical  change  indicates 
the  direction  in  which  the  change  will  proceed :  when  the 
possibility  of  evolution  of  heat  exists,  then  the  reaction  will 
proceed  in  such  a  direction  as  to  bring  this  about.  Take, 

31 


32  PHYSICAL  CHEMISTRY 

for  instance,  hydrogen  and  oxygen.  Two  grams  of  the 
former  with  sixteen  grams  of  the  latter  can  develop  69 
calories  when  uniting  to  form  water.  The  principle  just 
referred  to  sees  in  this  possibility  of  heat  development  the 
cause  of  the  formation  of  the  water,  which,  as  we  know, 
takes  place  when  the  mixture  of  the  gases  is  ignited.  Con- 
versely, if  we  consider  nitrogen  and  chlorine,  we  find  that  by 
their  union  no  heat  will  be  developed;  on  the  contrary, 
heat  will  be  absorbed.  So  here,  instead  of  a  union  of  the 
elements,  the  tendency  is  toward  the  decomposition  of  the 
compound.  When  the  union  has  been  achieved  by  indirect 
means,  decomposition  can  be  brought  about  by  the  slightest 
shock.  For  many  years  this  conception  was  a  fundamental 
principle  of  thermochemistry,  and  numberless  facts  were 
known  to  support  it. 

In  spite  of  this  it  is  not  difficult  to  furnish  examples  of 
cases  in  which  chemical  changes  take  place  with  absorption 
of  heat.  Freezing  mixtures,  like  that  of  hydrochloric  acid 
and  Glauber's  salt,  whose  operation  depends  on  the  accom- 
plishment of  a  chemical  change,  in  this  particular  case 

Na3S04  . 10H20  +  2HC1  ->  2NaCl  +  10H2O  -f  H2SO4, 

indicate  the  location  of  facts  which  contradict  this  "principle 
of  maximum  work."  The  greater  number  of  reactions 
which  proceed  only  to  a  certain  limit,  like  the  decomposition 
of  calcium  carbonate  which  ceases  when  a  certain  pressure 
of  carbon  dioxide  has  been  obtained,  likewise  involve  dis- 
proofs of  the  suggested  principle. 

Nevertheless,  the  expression  "maximum  work"  was  for- 


PURE  CHEMISTRY  33 

innately  chosen,  since  the  correct  principle  for  the  prediction 
of  reactions  must  connect  the  possibility  of  a  change  with 
the  possibility  of  a  concomitant  accomplishment  of  work. 
The  newer  conception  is  not  less  simple  than  the  older,  and 
is  in  a  measure  self-evident.  Whenever  any  change  whatever 
in  the  realm  of  nature  can  accomplish  work,  that  is,  can  over- 
come resistance,  it  must  proceed  when  the  resistance  is  absent. 
This  is  true  in  particular  of  chemical  changes.  Now,  it 
must  be  noted  that  the  accomplishment  of  work  and  the 
development  of  heat  in  chemical  changes  do  not  mean  quite 
the  same  thing.  Often  they  do  go  hand  in  hand,  as  in  the 
case  of  explosives  like  gunpowder  and  dynamite.  These 
materials  are  familiarly  known  to  furnish  by  their  explosion 
great  chemical  means  of  doing  work  and  at  the  same  time 
to  develop  large  quantities  of  heat.  A  compound  like 
phosphonium  chloride  (PH4C1),  however,  a  solid  body,  tends 
to  decompose  at  ordinary  temperatures  into  the  gases  phos- 
phine  (PH3)  and  hydrogen  chloride  (HC1)  with  marked 
absorption  of  heat.  Yet  the  decomposition  products  of  this 
action  may  exercise  a  pressure  of  some  twenty  atmospheres. 
Here  we  have  a  case  where  the  possibility  of  accomplishing 
work  does  not  coincide  with  the  capacity  to  develop  heat, 
and  yet  where  it  is  obviously  the  capacity  to  do  work  which 
controls  the  direction  of  the  change. 

The  great  difficulty  in  applying  this  new  principle  to  the 
prediction  of  reactions  lies,  however,  in  finding  a  method 
for  determining  from  other  data  the  existence  of  the  possi- 
bility of  accomplishing  work  and  the  amount  of  this  work 
in  any  given  action.  We  know  that  Berthelot  devoted  half 


34  PHYSICAL  CHEMISTRY 

of  his  life  to  the  systematic  measurement  of  heats  of  reac- 
tion. Trusting  in  his  principle  he  desired  to  present  chem- 
ists with  the  data  which  appeared  from  this  point  of  view  to 
be  suitable  for  the  prediction  of  chemical  changes.  Since  a 
change  in  the  fundamental  conception  itself,  however,  has 
been  shown  to  be  necessary,  another  magnificent  life  work  has 
been  suggested.  This  piece  of  research  would  require  the 
repetition  of  all  the  investigations,  carried  out  by  Berthelot 
with  the  calorimeter,  with  the  object  of  determining  the 
ability  of  each  reaction  to  do  work.  This  task  would  be, 
however,  incomparably  more  difficult  than  Berthelot's,  since 
the  possibility  of  accomplishing  work  depends  in  a  much 
greater  degree  on  the  conditions,  the  temperature,  and,  in 
the  case  of  dissolved  bodies,  the  concentration,  than  does 
the  heat  development.  This  fact  is  in  harmony  with  the 
great  influence  which  these  factors  exert  upon  chemical 
changes. 

Let  us  begin  with  a  very  simple  example  and  consider  the 
formation  of  carnallite  at  —  21°  according  to  the  simplified 
equation : 
MgCls  .  12H2O  +  KC1  =  MgCl2  .  KC1  .  6H2O  +  6H2O. 

Obviously,  at  —21°  the  possibility  of  doing  work  (E)  of 
which  the  formation  of  carnallite  is  capable,  is  zero. 

E  =  Q. 

Above  —21°  the  reaction  proceeds,  however.  It  can, 
therefore,  overcome  a  resistance,  and  since  the  reaction  is 
accompanied  by  increase  in  volume  this  resistance  might  be 
a  pressure.  The  maximum  work  will  obviously  be  obtained 


PURE  CHEMISTRY  35 

in  this  case  if  the  resistance  is  so  great  that  the  formation  of 
carnallite  is  just  able  to  take  place  and  no  more,  while  any 
increase  in  the  pressure  would  cause  a  reversal  of  the  change. 
Under  these  circumstances  the  transformation  is  reversible, 
and  thus  the  principle  of  reversible  cycles  can  be  applied 
to  it.  The  use  of  this  principle  leads  to  the  expression 

dE=    -W^- 
or  for  finite  values 


This  means  that  at  a  temperature  d  T  (or  A£)  degrees  above 
the  transition  point,  which  in  the  present  case  is  situated  at 
252°  on  the  absolute  scale,  an  amount  of  work  dE  (or  E) 
can  be  accomplished.  In  applying  this  formula,  since  W 
is  the  heat  of  formation  of  carnallite  by  the  action  repre- 
sented in  the  preceding  equation,  dE  and  W  must  be 
expressed  in  the  same  units,  for  example  calories. 

From  the  above  expression  the  most  essential  fact  may  be 
read  at  once.  At  the  transition  temperature  (A£  =  0)  E  has 
the  value  zero.  Above  and  below  this  the  sign  of  E 
changes.  Here  the  sensitiveness  to  changes  in  tempera- 
ture of  the  power  to  do  work  is  most  pronounced,  and  the 
sensitiveness  of  the  direction  of  the  chemical  change  to  the 
same  influence  is  most  noticeable. 

The  principle  of  Berthelot  now  appears  in  a  new  light. 
If  A/  =  —  T,  that  is  to  say,  if  the  absolute  zero  is  the  tem- 
perature of  experiment,  then 

E=W  . 


36  PHYSICAL  CHEMISTRY 

That  is  to  say,  under  these  circumstances,  the  heat  developed 
will  be  a  measure  of  the  capacity  to  do  work.  The  fact  that 
Berthelot's  principle  under  ordinary  conditions  so  frequently 
gives  satisfactory  results  depends  chiefly  on  the  fact  that  our 
ordinary  temperature  of  experiment  is  relatively  low,  being 
only  273  degrees  removed  from  the  absolute  zero.  In  the 
neighborhood  of  such  a  temperature  as  1000°  the  whole  cir- 
cumstances are  essentially  different  and  usually  the  results 
are  in  conflict  with  Berthelof  s  law.  Thus  at  that  tempera- 
ture acetylene  is  formed  with  absorption  of  heat,  and  water 
decomposes  in  spite  of  the  fact  that  its  formation  is  accom- 
panied by  the  evolution  of  heat. 

We  must  also  point  out  a  second  basis  for  the  measure- 
ment of  capacity  for  doing  work  which  has  been  extremely 
fruitful.  The  relation  of  this  capacity  to  do  work  to  the  pos- 
sible accomplishment  of  mechanical  work  has  already  been 
referred  to.  Then  we  noted  its  relation  to  heat  development. 
There  remains  still  for  consideration  its  relation  to  the  pro- 
duction of  electricity.  Take  a  chemical  change  which 
develops  electricity,  like  the  displacement  of  copper  by  zinc 
in  the  Daniell  cell, 

Zn  -f  CuSO4  -  ZnSO4  +  Cu  . 

This  reaction  can  just  as  well  be  overcome  by  a  suitable 
resistance  and  forced  to  proceed  in  the  reverse  direction,  as 
an  action  accompanied  by  increase  in  volume  can  be  reversed 
by  pressure.  Here,  however,  the  opposing  force  must  be  of 
an  electrical  nature.  As  a  matter  of  fact,  when  a  current  of 
electricity  is  applied  in  the  reverse  direction  to  a  Daniell 


PURE  CHEMISTRY  37 


cell  the  amount  of  chemical  change  is  at  once  diminished. 
The  change  can  be  brought  to  rest  completely  if  the  electro- 
motive force  of  the  contrary  current  is  equal  to  that  of  the 
cell ;  and  if  it  is  greater  the  direction  of  the  action  may  even 
be  reversed.  The  electromotive  force  when  electricity  is  pro- 
duced corresponds  therefore  to  the  pressure  when  the  chemi- 
cal change  tends  to  bring  about  an  increase  in  volume. 
Detailed  consideration  from  this  point  of  view  leads  us  to 
discover  in  the  electromotive  force  a  measure  of  the  capacity 
to  do  work. 

In  all  this  we  have  a  very  rich  field  for  working  out  the 
problem  of  predicting  reactions,  and  this  method  brings 
within  our  grasp  the  prediction  of  reactions  which  are  much 
less  simple  than  those  which,  like  the  formation  of  carnallite, 
are  characterized  by  a  transition  temperature,  and  whose 
whole  behavior  is  defined  when  a  single  temperature  is  given. 
In  this  way,  too,  the  more  delicate,  gradual  displacement  of 
a  condition  of  chemical  equilibrium  under  the  influence  of 
temperature  and  concentration  is  brought  under  control — a 
fact  which  has  recently  been  demonstrated  in  a  most  striking 
manner.1 

A  chemical  change  which  illustrates  this  is  the  action  of 
thallium  chloride  on  potassium  sulphocyanate  solution.  This 
takes  place  with  so-called  double  decomposition  according  to 
the  equation: 

T1C1  +  KSCN  =  T1SCN  +  KC1  . 

This  change  belongs,  however,  to  those  which  reach  a  con- 
dition of  rest  before  they  have  been  completely  accomplished, 

i  BBEDIG  UND  KNCPFFEB,  Zeit.f.  phystk.  Chem.,  Vol.  XXVI,  p.  260. 


38  PHYSICAL  CHEMISTRY 

and  lead  to  a  so-called  chemical  equilibrium.  This  we  repre- 
sent in  symbols  thus: 

T1C1  +  KSCN  ±5  T1SCN  +  KC1  . 

• 
The  condition  of  equilibrium  exists  not  only  at  a  definite 

temperature,  as  in  the  case  of  equilibria  having  transition 
points,  but,  as  the  temperature  changes,  is  displaced  grad- 
ually in  one  direction  or  the  other  with  a  corresponding 
alteration  in  the  concentrations  of  the  dissolved  chloride  and 
sulphocyanate  of  potassium. 

The  above  change  was  employed  for  the  construction  of  a 
galvanic  cell,  whose  electromotive  force  was  measured.  The 
changes  in  this  electromotive  force  brought  about  by  altera- 
tions in  temperature  and  concentration  were  studied.  From 
this  investigation  the  conditions  were  discovered  under  which 
the  electromotive  force  became  zero.  In  view  of  the  small 
solubility  of  the  thallium  salts,  this  depended  essentially  on 
the  concentration  of  the  chloride  and  sulphocyanate  of  potas- 
sium. In  a  simultaneous  study  of  the  conditions  when 
chemical  equilibrium  was  reached,  it  was  discovered  that 
they  corresponded  exactly  to  those  at  which  the  electromo- 
tive force  became  zero.  We  were  thus  furnished  with  the 
sharpest  possible  test  of  the  principle  involved. 

We  come  now  to  the  third  achievement  of  physical  chem- 
istry in  the  realm  of  pure  chemistry.  This  has  to  do  with 
the  nature  of  the  solutions  of  acids,  bases,  and  salts.  These 
have  been  called  electrolytes,  since  they  conduct  electricity, 
and  since  the  dissolved  substance  is  decomposed  into  two  so- 
called  ions.  At  the  one  pole  acids  give  hydrogen,  while  at 
the  other  (the  positive) .  the  rest  of  the  molecule  is  set  free. 


PURE  CHEMISTRY  39 


This  ion  in  the  case  of  oxygen  salts  usually  decomposes  with 
evolution  of  oxygen.     For  example: 


CuSO4  =  Cu  +  SO4  ,     and  SO4  =  SO3  -f  O  . 

The  application  of  Avogadro's  law  as  extended  to  solu- 
tions, especially  dilute  ones,  has  had  curious  consequences 
in  the  case  of  electrolytes.  It  appears  that  the  number  of 
dissolved  molecules  is  greater  than  that  corresponding  to  the 
smallest  possible  chemical  formulae,  such  as  CuSO4  or  HC1  in 
the  above  examples.  This  excess  in  the  number  of  molecules 
forces  us  almost  irresistibly  to  the  belief  in  a  genuine  decom- 
position. In  the  case  of  salts,  a  priori  considerations  might 
lead  us  to  the  inference  that  in  their  solutions  a  mixture  of 
the  acid  and  base  would  be  found.  If  this  were  the  case  no 
heat  change  would  be  perceptible  when  the  acid  and  base  in 
suitably  diluted  form  were  mixed,  since  no  formation  of  salt 
should  result.  As  a  matter  of  fact,  however,  experiments 
show  that  a  notable  production  of  heat  actually  occurs. 
Then,  too,  this  explanation  is  obviously  inapplicable  to  the 
solution  of  an  acid  or  of  a  base  by  itself. 

A  fortunate  release  from  this  dilemma  was  suggested  by 
Arrhenius  in  the  assumption  of  electrolytic  dissociation. 
This  assumption  consists,  as  is  well  known,  in  the  idea 
that  the  ions  which  are  liberated  when  the  solution  is 
decomposed  by  electricity  are  all  present  in  the  free  condi- 
tion before  the  application  of  the  current.  Their  presence 
is  not  perceived,  in  consequence  of  an  electrical  charge 
which  is  attached  to  them  and  which  they  lose  during 
electrolysis.  Thus,  in  dealing  with  hydrochloric  acid,  we 


40  PHYSICAL  CHEMISTKY 

can  see  that  the  dissolved  body  is  not  HC1,  but  a  mixture  of 
H  and  Cl,  that  is  to  say,  of  positively  charged  hydrogen  and 
negatively  charged  chlorine  atoms.  That  these  charges  of 
electricity  should  so  profoundly  alter  the  behavior  that 
neither  the  familiar  properties  of  hydrogen  nor  those  of 
chlorine  are  perceptible  in  the  hydrochloric  acid  solution, 
appears  at  first  sight  to  be  a  serious  objection.  On  closer 
consideration,  however,  we  see  that  this  conception  may  be 
accepted  as  a  possibility,  even  if  the  difficulties  have  not 
been  completely  cleared  up.  Over  against  this  ground  of 
hesitation  we  are  in  a  position  to  set  a  great  number  of  facts 
which  before  the  assumption  of  electrical  dissociation  were 
without  explanation.  Not  only  so,  but  this  theory  has  enabled 
us  to  foretell  chemical  occurrences  and  to  some  extent  account 
for  them  mathematically.  It  may  be  added  that  Raoult,  who 
has  devoted  himself  for  more  than  twenty  years  to  the  study 
of  dilute  solutions,  at  first  rejected  this  theory,  but  now 
fully  concurs  in  the  explanation  offered  by  Arrhenius. 

If  it  is  a  question  of  facts  of  a  qualitative  nature,  one 
has  only  to  put  forth  his  hand  in  any  direction.  Thus, 
chlorine  as  it  is  contained  in  electrolytes,  such  as  solutions 
of  hydrochloric  acid  and  its  salts,  which  according  to  this 
theory  contain  it  in  ionic  form,  behaves  in  an  entirely  differ- 
ent manner  from  the  element  as  it  is  found  in  compounds  of 
a  different  sort,  like  chloroform  and  chloral.  The  former 
with  silver  nitrate  give  silver  chloride  at  once,  the  latter  do 
not.  Again,  the  identity  in  the  color  of  the  different  salts 
of  rosaniline,  whether  we  take  the  nitrate,  hydrochloride, 
or  any  other,  finds  its  explanation  at  once  in  the  presence  of 


PURE  CHEMISTRY  41 

the  same  colored  ion.  The  smallest  change  in  this  colored 
ion,  however,  by  the  introduction  of  methyl,  for  example, 
produces  profound  and  much  prized  changes  in  tint.  Still 
again,  the  equal  optical  rotations  of  solutions  of  the  various 
salts  of  tartaric  acid  may  be  accounted  for  by  the  fact  that 
they  contain  the  same  optically  active  ion,  while  a  change 
in  this  ion  itself,  by  the  introduction  of  acetyl,  for  example, 
produces  instantly  a  marked  change  in  the  extent  of  the 
rotation. 

The  results  of  quantitative  measurement  are  not  less  con- 
vincing, although  unfortunately  always  limited  by  the  fact 
that  the  foundation  of  the  calculations,  the  extended  law  of 
Avogadro,  is  strictly  applicable  only  to  the  condition  of 
extremest  dilution.  The  limits  of  time  forbid  our  pursuing 
the  subject  in  greater  detail  in  this  direction.  I  simply 
mention  the  calculation  of  diffusion  speed  by  Nernst,  the 
calculation  of  the  variation  in  the  conductivity  of  distilled 
water  with  temperature  by  Kohlrausch,  and  the  calculation 
of  the  influence  of  concentration  on  the  behavior  of  organic 
acids  and  bases  by  Ostwald.  A  representative  compilation 
of  the  achievements  in  this  direction  was  presented  by 
Arrhenius  to  the  International  Congress  of  Physicists,  held 
at  the  Paris  Exposition  of  1900. 

Finally,  let  me  add  that  the  liquid  in  which  the  life 
functions  of  living  plants  and  animals  are  performed  is 
invariably  a  dilute  electrolyte.  For  this  reason  physiology 
and  medicine  have  promptly  taken  possession  of  these  new 
conceptions  and  the  consequences  even  of  their  earliest 
applications  have  been  most  significant. 


PHYSICAL  CHEMISTRY   AND  INDUSTRIAL 
CHEMISTRY 


LECTURE  IV 

PHYSICAL  CHEMISTRY  AND  INDUSTRIAL  CHEMISTRY1 

The  Co-operation  of  Physical  and  Industrial  Chemistry — Two  Illustra- 
tions to  Be  Discussed  —  Results  of  Scientific  Study  of  Carnal- 
lite  and  Possibilities  of  Their  Commercial  Application  to  the 
Manufacture  of  Potassium  Chloride — The  Recent  Discoveries  in 
Connection  with  Alloys  and  Steel,  Introduced  by  a  Description 
of  the  Peculiar  Behavior  of  Tin  and  its  Explanation — White  and 
Gray  Tin  and  Their  Transition  Point  at  20°— The  Methods  of 
Determining  the  Transition  Point  —  Use  of  the  Dilatometer — The 
Electrical  Method. 

IN  this  and  the'  following  lecture  I  purpose  dealing 
with  the  application  of  physical  chemistry  to  technical 
problems.  In  a  general  way,  it  may  be  said  that  since 
physical  chemistry  makes  it  possible  to  treat  the  problems 
of  pure  chemistry  in  a  new  manner  with  fruitful  results,  it 
follows  almost  of  necessity  that  this  influence  of  physical 
chemistry  must  be  beneficial  also  to  that  branch  of  industry 
which  is  founded  upon  chemistry.  It  may  be  that  in  America 
the  situation  is  different  from  what  it  is  in  Germany. 
Naturally  I  am  insufficiently  acquainted  with  the  former, 
but  I  have  been  credibly  informed  during  my  stay  here 
that  in  the  industrial  world  the  idea  prevails  that  what  can 
be  done  on  a  small  scale  in  a  laboratory  experiment  cannot 

1  At  the  time  this  lecture  was  held,  XNIETSCH'S  concise  description  of  the  con- 
tract process  for  the  manufacture  of  sulphuric  acid  had  not  yet  been  given.  I  refer 
the  reader  therefore  to  his  exceedingly  interesting  communication.  Her.  d.  deutsch. 
chem.  GeselL,  Vol.  XXXIV,  p.  4069  (cf.  also  SACKUB,  ZeitschriftfiirElektrochemie^ol. 
VIII,  p.  77). 

45 


46  PHYSICAL  CHEMISTEY 

be  accomplished  on  a  large  scale  in  the  factory.  Of  course 
there  is  naturally  a  difference  between  laboratory  experimen- 
tation and  technical  investigation.  In  the  laboratory  it  makes 
no  difference  whether  the  process  pays  or  not,  while  this  is 
precisely  the  most  important  question  in  the  works.  Aside 
from  this,  however,  one  may  state  with  confidence  that  what 
occurs  in  a  test-tube  can  also  be  done  with  hundredweights 
of  material,  provided  the  conditions,  for  example  of  tempera- 
ture, are  exactly  imitated.  The  factory  has,  of  course, 
resources  so  much  beyond  those  of  most  laboratories  that 
the  imitation  of  laboratory  conditions  on  a  large  scale 
is  only  a  question  of  care.  It  is  possible,  however,  that  my 
informant  did  not  reproduce  the  opinion  in  America  on  this 
point  correctly. 

There  exists  in  Germany  a  very  beneficial  co-operation 
between  laboratory  work  and  technical  work.  Both  go  as 
far  as  possible  hand  in  hand.  After  physical  chemistry  had 
made  several  important  advances  and  was  firmly  established 
in  such  a  way  that  pure  chemistry  was  assisted  by 
co-operation  with  it,  Ostwald  judged  correctly  that  this 
co-operation  would  also  be  valuable  in  technical  directions. 
In  this  belief  about  eight  years  ago  he  founded  the  Electro- 
chemical Society,  of  which  I  happen  at  the  present  moment  to 
have  the  honor  of  being  president.  I  may  add  that  in  those 
eight  years  this  society,  whose  chief  object  was  to  bring 
together  the  men  of  pure  science  and  the  representatives  of 
technical  science,  has  succeeded  in  gathering  six  hundred 
members.  All  the  most  conspicuous  chemical  industries  of 
Germany  and  other  countries  are  represented  in  the  society. 


INDUSTRIAL  CHEMISTRY  47 

The  society  possesses  in  addition  its  own  organ  of  publica- 
tion, the  Zeitschrift fur  Elektrochemie.  At  the  last  general 
meeting  in  Freiburg  in  Baden  the  desirability  of  expanding 
the  society  was  discussed  in  order  that  the  co-operation 
between  technical  and  scientific  chemistry  might  not  be  con- 
fined to  the  territory  of  electrochemistry.  It  seemed  pos- 
sible to  include  physical  chemistry  as  a  whole,  so  far  as  parts 
of  the  subject  other  than  this  one  had  already  found  appli- 
cation or  appeared  to  be  capable  of  finding  it.1 

Nor  has  the  stimulus  to  this  co-operation  its  source  purely 
on  the  scientific  side.  That  it  comes  from  both  parties  may 
be  seen,  for  example,  in  the  fact  that  a  year  ago  Professor 
Goldschmidt,  at  that  time  the  representative  of  physical 
chemistry  in  Heidelberg,  was  asked  by  the  directors  of  the 
Badische  Anilin-  and  Sodafabrik  to  give  a  series  of  lectures 
on  this  branch  of  the  science  before  the  chemists  of  the 
factory,  and  did  so  with  great  success.  That  an  opening  up 
of  new  points  of  view  in  the  treatment  of  practical  problems 
was  expected  to  flow  from  these  lectures  rather  than 
immediate  practical  results,  is  evident  when  we  consider  the 
present  purely  empirical  treatment  of  problems  affecting 
industrial  chemistry.  Ultimately,  however,  direct  results  of 
its  influence  must  appear  without  fail. 

In  selecting  for  discussion  industries  in  which  the  appli- 
cation of  physical  chemistry  may  be  most  useful,  we  turn 
naturally  once  more  to  the  inorganic  side.  In  this  direction, 
as  we  have  already  remarked,  physical  chemistry  is  most 

i  As  the  result  of  this  discussion  the  society  is  now  known  as  the  "Deutsche 
Bunsen-Gesellschaft  fur  angewandte  physikalische  Chemie.'1  [A.  S.] 


48  PHYSICAL  CHEMISTRY 

easy  to  apply.  In  the  first  place  I  mention  the  treatment  of 
the  salts  at  Stassfurt,  where  the  problem  concerns  the  treat- 
ment of  deposits  which  must  be  considered  the  results  of  the 
evaporation  of  sea- water.  The  substances  concerned  are  the 
chlorides  and  sulphates  of  sodium,  potassium,  magnesium, 
and  calcium.  The  study  of  these  salts  and  of  their  solubility- 
relationships,  recently  resumed,  and  this  time  from  the 
physico-chemical  standpoint,  may  be  expected  to  have  some 
influence  on  their  treatment  for  manufacturing  purposes.  In 
the  second  place  we  may  name  the  field  of  metallurgy,  par- 
ticularly alloys  and  steel.  The  study  of  these  subjects  in  the 
same  fashion,  as  has  been  stated  by  those  with  authority  to 
speak  on  the  subject,  is  likely  to  lead  to  a  new  epoch  in 
siderology.  The  practical  applications  of  electro-chemistry, 
which  are  being  developed  at  Niagara,  and  in  an  especial 
degree  also  the  use  of  so-called  catalyzers,  that  is  to  say, 
substances  which  increase  the  speed  of  reaction  of  chemical 
changes,  like  platinum  in  the  new  method  of  making  sul- 
phuric acid,  likewise  furnish  an  opportunity  for  the  fruitful 
employment  of  physical  chemistry.1  A  few  examples  will 
illustrate  these  possibilities. 

Let  us  begin  with  the  salt  industry  and  linger  for  a 
moment  once  more  to  continue  the  discussion  of  carnallite, 
which  has  the  composition  KC1 .  MgCl2  .  6H2O,  and  is  well 
known  to  be  one  of  the  most  important  commercial  sources 
of  potassium  compounds. 

The  treatment  of  this  double  salt  depends  essentially  upon 

1  As  the  proofs  of  this  work  are  being  corrected  I  hear  of  the  founding  of  an 
American  Electrochemical  Society,  which  according  to  the  program  of  addresses 
has  the  object  of  assisting  in  such  applications. 


INDUSTRIAL  CHEMISTRY  49 

the  fact  that,  when  the  mineral  is  brought  in  contact  with 
water,  the  magnesium  chloride  goes  for  the  most  part  into 
solution,  while  the  potassium  chloride  remains  in  the  solid 
form.  When  the  liquid  has  been  saturated  with  carnallite 
the  composition  of  the  solution  at  25°  is  expressed  by  the 

formula 

[1000H2O  +  11KC1  +  73MgCl2]  .' 

The  action  of  water  in  this  case,  therefore,  corresponds  with 
the  equation: 

73(KC1 .  MgCl2  .  6H20)  +  562H2O  = 

[1000H2O  +  11KC1  +  73MC1J  +  62KC1  . 

When  this  saturated  solution  is  concentrated,  carnallite 
crystallizes  out  until  finally  chloride  of  magnesium  begins 
to  appear.  At  25  °  this  takes  place  when  the  composition  of 
the  solution  has  become 

[1000H2O  +  2KCl  +  105MgCl2]  . 

The  result  of  this  concentrating  process,  therefore,  is 
expressed  by  the  equation: 

[1000H2O  +  11KC1  +  73MgCla]=339H2O+9.8(KCl.  MgCl2  . 
6H2O)  +  0 . 6[1000H2O  +  2KC1  +  105MgCl2]  . 

The  final  liquid  is  thus  essentially  a  solution  of  magnesium 
chloride.  The  carnallite  which  has  crystallized  out  can  be 
treated  with  water  as  before.  The  disposition  of  the  mag- 
nesium chloride  mother-liquor,  so  as  to  avoid  the  contamina- 
tion of  river  waters,  appears  to  be  a  problem  of  no  little 
difficulty. 

i  In  what  follows,  symbols  representing  the  composition  of  solutions  are  placed 
within  square  brackets. 


50  PHYSICAL  CHEMISTRY 

The  re-examination  of  the  carnallite  problem  from  the 
physico-chemical  standpoint,  which  we  have  discussed  in  the 
previous  lecture,  possesses  the  advantage  that  it  shows  at 
one  glance  all  the  possible  methods  of  splitting  carnallite. 
The  one  just  referred  to  takes  its  place  as  a  special  case. 
As  a  result  of  this  more  general  treatment,  however,  two 
other  processes  emerge  and  are  to  be  considered  as  possi- 
bilities, even  in  the  matter  of  technical  application.  One 
of  these  is  founded  on  a  transformation  of  carnallite  in 
which,  below  —  21°,  it  takes  up  water  and  forms  potassium 
chloride  and  the  dodecahydrate  of  magnesium  chloride. 
Working  under  these  conditions  the  reproduction  of  about 
14  per  cent,  of  the  original  carnallite  which  occurs  in  the 
process  at  present  in  use  would  be  avoided.  After  satura- 
tion with  carnallite  and  separation  of  potassium  chloride,  a 
solution  would  be  formed  of  the  composition 

[1000H2O  +  10KC1  +  66MgCl2]  . 

From  this,  by  concentrating  or  cooling,  magnesium  chlo- 
ride with  twelve  molecules  of  water  of  crystallization  and 
potassium  chloride  would  be  deposited.  A  second  possibil- 
ity of  obtaining  potassium  chloride  is  indicated  by  the 
decomposition  of  carnallite  at  168°.  In  this  case  three- 
quarters  of  the  potassium  chloride  is  separated,  and  one- 
quarter,  with  all  the  magnesium  chloride  and  water,  may 
be  poured  off  in  fluid  form.  The  operation  must  of 
course  be  conducted  in  closed  vessels,  since  the  pressure  of 
the  water  of  crystallization  in  carnallite  at  168°  is  greater 
than  one  atmosphere.  If  this  liquid  is  separated  from  the 


INDUSTRIAL  CHEMISTRY  51 

solid  potassium  chloride  by  some  sort  of  filter  press,  and  is 
lowered  in  temperature  to  115°,  the  potassium  chloride  still 
contained  in  it  reappears  in  the  form  of  carnallite.  The  hot 
solution  now  remaining  can  again  be  separated  from  the 
solid  by  pressure,  and  is  an  almost  pure,  melted  hydrate  of 
magnesium  chloride,  free  from  potassium  compounds. 

In  the  technical  point  of  view  a  good  deal  may  be  said  in 
favor  of  the  last  process.  A  decomposition  of  the  carnallite 
(without  the  formation  of  any  mother-liquor)  takes  place,  in 
the  course  of  which  three-fourths  of  the  potassium  chloride 
as  such  and,  in  the  final  step,  a  corresponding  amount  of  solid 
magnesium  chloride  are  obtained,  while  a  quarter  of  the  car- 
nallite is  recovered  unchanged  and  can  be  worked  up  afresh. 
Thus,  what  in  the  ordinary  process  is  attained  by  the  use  of  a 
solvent  and  by  taking  advantage  of  solubilities  is  here 
reached  by  changes  in  temperature  and  the  accompanying 
phenomena  of  transition  or  of  melting  and  solidification. 
How  far,  however,  a  remunerative  process  is  involved  in  this 
can  be  shown  by  future  study  only.  So  much  we  know, 
that  the  operation  as  it  may  be  carried  out  in  the  laboratory 
with  a  few  grams  has  also  been  found  to  work  in  the  factory 
when  several  kilograms  are  used.  The  applicability  of  the 
method  on  a  large  scale  is  thus  assured,  as  we  might  have 
expected.  The  question  of  cost  alone  remains  open. 

As  a  second  example,  I  desire  to  discuss  the  applica- 
tion of  physical  chemistry  in  the  field  of  metallurgy.  By 
far  the  most  important  illustration  in  this  direction  is  in 
connection  with  the  manufacture  of  steel  and  the  explanation 
of  its  peculiarities.  Authorities  in  this  subject  admit  on  all 


52  PHYSICAL  CHEMISTRY 

hands  that  physical  chemistry  has  thrown  a  most  welcome 
light  on  the  complicated  phenomena  presented  by  the 
behavior  of  steel.  These  of  course  primarily  depend  upon 
the  interactions  of  iron  and  carbon.  The  interactions,  how- 
ever, are  complicated  by  the  fact  that  transformations  occur 
both  in  the  iron  and  in  those  constituents  which  contain  both 
carbon  and  iron.  It  will  simplify  the  matter  greatly,  there- 
fore, if  we  first  consider  the  changes  which  occur  in  a  single 
metal.  We  may  take  tin  as  being  the  metal  in  connection 
with  which  changes  of  this  kind  have  been  most  com- 
pletely investigated. 

The  remarkable  fact  in  the  behavior  of  tin  to  which  I 
ask  your  attention  was  discovered  long  ago.  Careful  his- 
torical investigation  has  demonstrated  that  even  Aristotle 
was  acquainted  with  the  fact,  whose  explanation  has  so 
recently  been  brought  to  light.  The  fact  referred  to  is  that 
common  tin  is  capable  of  undergoing  a  profound  change 
which  amounts  to  a  complete  disguise.  The  product  of  this 
change,  for  reasons  which  we  shall  learn  later,  cannot  be 
exhibited  to  you,  and  I  must  therefore  content  myself  by 
showing  a  photograph  of  a  piece  of  tin  which  is  under- 
going this  transformation  (Fig.  4).  The  impression  which 
examination  of  this  piece  of  tin  makes  is  that  of  an  object 
which  has  been  overtaken  by  some  disease.  As  a  matter  of 
fact,  indeed,  the  phenomenon  has  this  in  common  with  dis- 
ease, that  it  is  contagious.  When  the  phenomenon  exhibits 
itself,  as  it  sometimes  does,  in  the  pipes  of  church  organs,  it 
is  consequently  a  good  plan  to  remove  the  objects  which 
have  become  infected.  The  disintegration  into  a  gray 


or  THE 
UNIVERSITY 

OF 


INDUSTRIAL  CHEMISTRY  53 

powder,  which  marks  the  progress  of  the  attack,  proceeds 
gradually  until,  especially  in  the  case  of  thin  bodies  like 
organ  pipes,  the  object  has  been  completely  destroyed.  We 
must  not  delay  to  add  that,  in  spite  of  appearances,  the 
change  is  not  due  to  the  influence  of  the  atmosphere  or  its 
moisture.  On  the  contrary,  the  tin  undergoes  the  change 
all  by  itself,  and  the  gray  product  has  only  to  be  heated  in 
order  that  without  change  of  weight  it  may  be  reobtained  in 
the  original  metallic  form.  It  is  precisely  on  account  of  the 
influence  of  heat  on  the  change  that,  at  the  temperature 
which  we  are  at  present  experiencing,  I  am  unable  to  show 
this  so-called  gray  tin. 

We  owe  particularly  to  Schaum l  and  Cohen2  our  knowl- 
edge of  the  conditions  which  influence  this  extraordinary 
change.  The  conclusion  is  that  the  whole  phenomenon  is  related 
to  a  definite  temperature,  namely  20°  C.  Below  this  tem- 
perature the  formation  of  gray  tin  can  occur,  while  only 
above  this  temperature  is  the  formation  of  the  common  variety 
possible.  The  temperature  limit  20°,  commonly  known  as 
the  transition  point,  separates  two  ranges  of  temperature  in 
which  the  gray  and  the  white  tin  respectively  are  stable.  It 
exhibits  thus  a  certain  analogy  to  a  melting-point,  with  this 
sole  difference  that  at  a  melting-point  a  so-called  change  of 
state  occurs.  In  the  latter  case  the  bodies  are  solid  and 
liquid  respectively.  The  temperature  0°,  for  instance,  can 
be  named  the  transition  point  of  ice  and  water.  Along  with 
this  analogy  between  the  two  kinds  of  phenomena,  which  by 

l  Liebig's  Annalen,  Vol.  CCCVIII,  p.  29. 
iZeitschr.f.  physik.  Chem.,  Vol.  XXX,  pp.  601,  623. 


54  PHYSICAL  CHEMISTRY 

the  way  were  compared  even  by  Aristotle,  one  striking  differ- 
ence is  to  be  noticed.  This  difference  probably  accounts  for 
the  fact  that  the  limiting  temperature  of  20°,  which  sepa- 
rates gray  from  white  tin,  was  not  discovered  until  the  new 
methods  of  physical  chemistry  became  available.  This  nota- 
ble difference  lies  in  the  extreme  slowness  of  the  change  in 
the  case  of  tin.  Indeed,  the  change  may  fail  to  put  in  an 
appearance  for  years.  In  the  case  of  ice  and  water,  on  the 
other  hand,  superheating  of  ice  even  for  a  moment  seems  to 
be  impossible,  and  although  overcooling  of  water  beyond 
0°  can  occur,  the  slightest  touch  with  ice  destroys  the 
overcooling  instantly,  and  causes  freezing.  In  the  case  of 
tin  almost  every  possible  means  must  be  used  to  bring  the 
change  about,  at  all  events  when  the  temperature  of  experi- 
ment is  not  too  far  removed  from  20°. 

If  this  reluctance  to  change  did  not  exist,  the  tempera- 
ture of  transformation  could  be  observed  like  a  melting-point. 
It  could  be  followed  with  the  assistance  of  a  thermometer, 
for,  in  close  analogy  to  the*  phenomenon  of  melting,  the  for- 
mation of  white  from  gray  tin  is  accompanied  by  the  disap- 
pearance of  heat.  The  extreme  slowness  of  the  process, 
however,  renders  the  employment  of  other  means  necessary. 
I  shall  describe  two  of  them.  Before  doing  so,  however,  I 
should  remark  that  delayed  processes  of  this  kind  are  in 
general  more  common  in  connection  with  chemical  trans- 
formations than  in  physical  changes  of  state,  even  though 
the  latter  are  often  closely  analogous  to  the  former. 

One  of  the  methods  makes  use  of  the  very  notable  change 
in  volume  which  accompanies  the  transformation  of  the  tin. 


INDUSTRIAL  CHEMISTRY  55 

Ordinary  tin  has  a  specific  weight  of  7.3,  while  in  the  case 
of  gray  tin  this  constant  has  the  value  5.8.  Thus,  white  tin 
expands  more  than  a  quarter  in  undergoing  the  change.  An 
alteration  in  volume  like  this  can  be  very  easily  studied  by 
the  help  of  a  dilatometer.  This  instrument  is  a  kind  of 
thermometer  of  rather  large  dimensions.  Its  reservoir  is 
packed  with  the  substance  under  investigation — in  this 
case  the  tin.  After  the  reservoir,  which  originally  was 
open  for  the  reception  of  the  contents,  has  been  closed, 
the  air  is  pumped  out,  and  a  suitable  liquid  is  admit- 
ted. The  changes  in  the  level  of  this  liquid  in  the 
capillary  tube  serve  as  an  indication  of  the  alterations  in 
volume  which  occur  in  the  contents  of  the  reservoir,  and 
can  be  read  off  with  the  help  of  a  scale.  Without  special 
precautions,  however,  the  object  could  not  be  attained  by 
these  means  alone,  since,  without  stimulus,  the  transfor- 
mation often  fails  altogether  to  occur.  The  chief  among 
the  necessary  conditions  is  that  both  kinds  of  tin  inti- 
mately mixed  should  be  introduced  into  the  instrument. 
This  intimate  contact  serves  to  stimulate  either  transfor- 
mation, so  that  the  sensitiveness  of  the  arrangement  is  great- 
est when  equal  quantities  of  the  two  bodies  are  present. 
An  additional  expedient  is  indispensable  in  the  present  case. 
The  liquid  used  for  filling  the  apparatus  must  be  capable  of 
dissolving  to  the  greatest  possible  extent  the  body  which  is 
undergoing  the  change.  A  solution  of  pink-salt  (SnCl4  . 
2NH4C1)  has  been  found  most  suitable.  The  tin  dissolves 
in  this  substance  with  the  formation  of  stannous  chloride. 
That  one  of  the  two  transformations  which  under  the  given 


56  PHYSICAL  CHEMISTRY 

conditions  tends  to  occur,  is  brought  about  through  media* 
tion  of  this  process  of  solution.  One  modification  dissolves 
and  the  other  is  deposited.  Working  in  this  fashion 
the  dilatometer,  when  kept  at  a  constant  temperature,  shows 
the  transformation  in  one  direction  or  the  other  in  admir- 
able, if  somewhat  leisurely,  fashion.  For  example,  a  gradual 
increase  in  volume,  which  may  continue  for  days,  is  observed 
at  19°.  On  the  other  hand,  a  slow  contraction  occurs  at 
21°.  At  20°  the  system  remains  at  rest,  and  thus  the 
transition  temperature  is  determined  within  one  degree. 

While  applications  of  the  method  the  description  of  which 
we  have  just  concluded  always  occupies  several  days  or  even 
weeks,  a  second  plan,  which  is  now  to  be  mentioned,  has  the 
great  advantage  that  the  determination  of  the  transition 
temperature  can  be  made  in  a  short  time  and  with  much 
greater  accuracy.  The  second  method  makes  use  of  the 
electrical  currents  which  under  suitable  circumstances  are 
produced  by  the  transformations  of  the  two  forms  of  tin. 
The  apparatus  itself  is  again  very  simple.  It  consists  of  two 
short,  rather  thick-walled  test-tubes,  which  are  connected  by 
a  siphon  or  a  cross-piece  opening  into  the  side  of  each.  In 
one  of  the  tubes  some  gray  tin  is  placed,  and  in  the  other 
some  white  tin.  Metallic  contact  with  the  material  is  made 
by  means  of  two  platinum  wires  fused  into  the  bottoms  of 
the  test-tubes.  These  form  the  poles  of  a  cell  and  are  con- 
nected with  a  very  delicate  galvanometer.  The  circuit  is 
closed  by  means  of  pink-salt  solution,  with  which  the  two 
test-tubes  and  the  siphon  or  cross-piece  are  filled.  When  the 
temperature  is  not  far  from  20°  a  direct  transformation  of 


INDUSTRIAL  CHEMISTRY  57 

the  specimens  of  tin  does  not  occur.  The  only  consequence 
of  the  tendency  to  change  is  that  on  the  one  side  the  modi- 
fication which  is  unstable  at  the  existing  temperature  passes 
into  solution,  while  the  metal  in  the  other  test-tube  increases 
by  deposition.  Since,  however,  this  deposition  can  occur 
only  with  the  assistance  of  the  positive  ions  of  tin,  the  mass 
of  tin  which  is  increasing  in  quantity  acquires  a  positive 
charge,  while  the  other,  which  is  furnishing  positive  ions  to 
the  solution,  is  losing  an  equivalent  charge.  The  current 
which  is  produced  in  this  fashion,  and  whose  existence  and 
direction  may  be  foretold,  can  actually  be  observed.  In  con- 
sequence of  the  delicacy  of  electrical  measurements,  it  fur- 
nishes a  very  exact  indication  of  the  direction  in  which  the 
transformation  is  proceeding.  The  formation  of  the  gray  tin 
produces  a  current  in  one  direction,  that  of  the  white  in  the 
opposite  direction.  The  transition  temperature  is  indicated 
by  a  reversal  of  the  poles. 


LECTURE  V 

PHYSICAL  CHEMISTRY  AND  INDUSTRIAL  CHEMISTRY 

Results  of  the  Physico-Chemical  Study  of  Wrought  Iron,  Cast  Iron, 
and  Steel  —  Complications  Introduced  by  the  Presence  of  Carbon 
and  by  the  Occurrence  of  Solid  Solutions— Method  of  Studying  Iron 
by  Polishing,  Etching,  and  the  Use  of  the  Microscope  —  Constitu- 
ents are  Ferrite,  or  Pure  Iron;  Martensite,  or  the  Solid  Solution  of 
Carbon  in  Iron;  Cementite,  or  the  Carbide  of  Iron;  Graphite,  or 
Free  Carbon;  Pearlite,  or  the  Cryohydratic  Mass  —  Two  Forms  of 
Ferrite  with  Transition  Point  at  850°— Pearlite,  a  Mixture  of 
Cementite  and  Ferrite,  and  its  Formation  and  Composition— 
Hard  Steel  is  Overcooled  Martensite  — The  Graphite  — The  Be- 
havior of  Melted  Iron  Rich  in  Carbon — Rapid  Cooling  Gives  White 
Cast  Iron  Containing  Much  Cementite  —  Slow  Cooling  Gives  Gray 
Cast  Iron  by  Decomposition  of  the  Cementite  and  Production  of 
Graphite,  and  Finally  Pearlite — A  Numerical  Illustration  of  the 
Behavior  of  Molten  Iron  Containing  6%  per  Cent,  of  Carbon  When 
Cooled  (1)  Rapidly  and  (2)  Slowly. 

I  SHOULD  like  to  employ  the  second  hour  which  is  to  be 
devoted  to  the  application  of  physical  chemistry  to  techni- 
cal chemistry,  in  giving  you  some  conception  of  what  it  has 
done  for  the  study  of  iron.  Under  this  term  we  include  not 
only  wrought  iron,  but  also  cast  iron  and  steel,  which  are 
forms  of  iron  containing  more  or  less  carbon.  I  would  call 
your  attention  first  to  the  fact  that  von  Juptner,  one  of  the 
most  noted  authorities  on  steel,  has  described  the  results  of 
this  study  as  establishing  an  epoch  in  the  iron  industry.  In 
recognition  of  this,  his  recent  work  on  siderology  is  furnished 
with  an  introduction  of  sixty -one  pages  dealing  with  the  laws 

.of  solution. 

58 


INDUSTRIAL  CHEMISTRY  59 

The  behavior  of  steel  in  particular  is  far  from  simple,  and 
so  yesterday  I  prepared  for  the  introduction  of  this  subject 
by  explaining  the  simpler  but  somewhat  analogous  behavior 
of  tin.  Tin,  like  iron,  is  a  metal,  but,  while  in  the  case  of 
the  former  we  have  a  single  substance  occurring  in  different 
modifications,  when  we  approach  the  study  of  the  forms  of 
the  latter  which  are  of  technical  importance,  we  find  that  the 
carbon  which  is  present  plays  a  very  important  part.  In 
spite  of  this  complication,  the  new  physico-chemical  method 
of  treating  such  problems  has  illuminated  successfully  a 
rather  confusing  set  of  phenomena.  It  has  made  it  possible 
to  represent  the  whole  behavior  of  carboniferous  iron  by 
means  of  one  diagram,  inspection  of  which  enables  us  to  grasp 
the  essential  features  at  one  glance. 

A  second  introductory  explanation  is  necessary.  In  the 
case  of  tin,  the  peculiar  occurrence  of  a  metal  in  different 
forms  and  the  laws  governing  the  transformation  of  these 
were  emphasized.  In  the  case  of  iron  in  its  different  condi- 
tions this  phenomenon  recurs,  but  a  second,  consisting  in  the 
appearance  of  so-called  solid  solutions,  has  also  to  be  noticed. 

The  grasp  which  we  have  obtained  of  the  nature  of  ordi- 
nary fluid  solutions  has  been  so  fruitful  and  its  influence  so 
far-reaching  that  the  attempt  has  been  made  to  proceed  one 
step  farther  and  to  apply  the  same  conceptions  to  substances 
in  the  solid  condition.  We  are  certainly  entitled  to  speak 
of  solid  solution  in  certain  definite  cases,  where  the  complete 
homogeneity  combined  with  the  possibility  of  varying  com- 
position, which  are  characteristic  of  the  state  of  solution,  are 
found.  In  colored  specimens  of  glass  and  in  isomorphous 


60  PHYSICAL  CHEMISTRY 

mixtures,  of  two  alums  for  example,  we  are  just  as  little  able, 
even  with  the  help  of  the  microscope,  to  perceive  the  presence 
of  more  than  one  substance,  as  in  a  solution  of  sugar  in  water. 
It  is  a  familiar  fact  that  the  ordinary  colorless  alum,  when  crys- 
tallizing from  solutions  containing  the  highly  colored  chrom- 
alum,  forms  octahedra,  more  or  less  tinted  with  chrom-alum. 
And  yet  the  most  minute  observation  reveals  no  gross  irre- 
gularities in  the  physical  distribution  of  the  material,  or  any 
other  evidence  of  lack  of  homogeneity.  In  such  a  case,  there- 
fore, we  speak  of  the  existence  of  a  solid  solution.  When  the 
substance  is  amorphous,  as  in  the  case  of  colored  glass,  the 
analogy  to  a  fluid  solution  is  so  complete  that  the  two  are 
connected  by  a  series  of  more  or  less  viscous  mixtures  in 
such  a  way  that  no  sharp  distinction  can  be  drawn.  Of 
course,  when  the  solid  solution  is  crystalline  it  must  be 
admitted  that  it  differs  from  a  fluid  solution  fundamentally, 
in  so  far  that  an  arrangement  of  the  molecules  according  to 
some  definite  order  has  taken  place. 

The  essential  point  is  that  the  laws  of  fluid  solutions  have 
been  successfully  applied  to  solid  ones,1  and  that  this  appli- 
cation has  thrown  light  upon  the  behavior  of  varieties  of  iron 
containing  carbon. 

Passing  now  from  these  preliminary  statements  in  regard 
to  tin  and  solid  solutions,  let  us  take  up  the  main  subject. 
The  first  thing  to  be  noticed  is  that,  while  in  the  case  of  tin 
only  two  forms  had  to  be  considered,  there  are  here  more 
than  two.  In  the  industrial  point  of  view  there  are  three 
forms  of  iron  —  wrought  iron^  steel,  and  cast  iron  —  which 

tJber  feste  Lflsungen;"  AHRENS,  Sammlung  chemisch-technischer  For- 


tr&ge,  1900. 


INDUSTRIAL  CHEMISTBY  61 

differ  from  one  another  by  containing  proportions  of  carbon 
increasing  in  the  order  given.  Obviously,  too,  the  propor- 
tion of  carbon  is  not  the  only  thing  to  be  considered.  This 
is  demonstrated  by  the  change  produced  by  chilling  and 
hardening  steel,  which  results  from  more  or  less  rapid  cool- 
ing following  upon  elevation  to  some  definite  temperature 
and  occurs  without  any  alteration  in  composition.  On  this 
account  the  investigation  of  iron  demands  not  only  analysis 
but  also  microscopic  study.  The  specimen  is  first  polished 
and  then  etched  by  the  use  of  a  solution  of  hydrogen 
chloride  in  alcohol.  Sometimes  continued  polishing  with 
emory  and  a  plate  of  rubber  is  employed  to  secure  a  slight 
elevation  of  the  harder  parts  above  the  more  easily  abraded, 
softer  places.  In  either  case,  such  a  specimen,  when 
studied  microscopically  so  that  the  light  falls  upon  it 
obliquely,  shows  peculiarities  of  structure  which  permit  of 
further  differentiation  of  the  constituents.  As  a  result  of 
this  we  speak  of  ferrite,  which  is  pure  iron,  of  martensite, 
which  is  carboniferous  iron  of  varying  composition  but  homo- 
geneous structure  (the  solid  solution),  and  of  cementite,  a 
compound  of  iron  and  carbon  corresponding  to  the  formula 
Fe3C.  Besides  these,  pure  carbon  in  the  form  of  graphite, 
and  sometimes  of  diamond,  is  discoverable.  A  fifth  con- 
stituent is  pearlite,  a  carboniferous  iron,  heterogeneous  in 
structure,  but  possessing  a  constant  composition.  It  may  be 
that  still  other  forms  should  be  discriminated,  but  their  exist- 
ence has  not  yet  been  determined  with  perfect  certainty.1 

i  BAKHUIS-ROOSEBOOM,  Zeitschr.  f.  physik.  Chemie,  Vol.  XXXTV,  p.  437; 
BENEDICKS,  ibid..  Vol.  XL,  p.  545 ;  STANSFIELD,  Journal  of  the  Iron  and  Steel  Insti- 
tute, 1900,  Vol.  II. 


62  PHYSICAL  CHEMISTRY 

Beginning  with  pure  iron  (ferrite),  I  mention  first  a  fact 
determined  by  Le  Chatelier.  He  found  that,  like  tin,  iron 
exists  in  two  forms,  whose  transformation  is  dependent  upon 
a  definite  temperature,  which  in  this  case  is  850°.  These 
two  forms  we  shall  distinguish  as  a-ferrite  and  /3-ferrite. 
That  which  is  stable  in  the  cold,  and  in  general  below  850°, 
is  a-ferrite.  Soft  wrought-iron  which  has  been  freed  as  far 
as  possible  from  carbon,  as,  for  example,  piano-wire,  is  of 
this  kind.  We  record  this  first  fact  in  the  diagram,  Fig.  5, 
in  which  the  temperature  is  read  along  the  axis  of  abscissae 
and  the  content  of  carbon  along  the  axis  of  ordinates. 

The  second  fact  which  must  be  noted  is  that  /3-iron  is 
capable  of  taking  up  carbon  in  solid  solution,  while  a-iron 
does  not  possess  this  property.  Recalling  the  analogy 
between  transition  temperatures  and  melting-points,  and  the 
additional  conception  of  solid  and  fluid  solutions,  we  per- 
ceive that  the  addition  of  carbon  to  /8-iron  will  depress  the 
temperature  of  transformation,  just  as  dissolved  substances 
lower  the  freezing-point  of  melted  bodies.  Yon  Jiiptner 
has  even  applied  the  laws  of  fluid  solutions  to  calculation  of 
the  extent  of  this  depression.  Graphically  this  depression 
is  expressed  by  a  line  proceeding  from  the  point  850°  on  the 
horizontal  axis  and  ascending  to  the  left  in  correspondence 
with  the  lowering  in  temperature  and  increasing  content  of 
carbon. 

Just  as  a  melting-point  cannot  be  depressed  without 
limit  by  the  addition  of  soluble  substances,  so  is  it  with  the 
transformation  temperature  of  a  solid  solution  like  this.  As 
the  solvent  gradually  freezes  out  of  a  fluid  solution,  the 


INDUSTRIAL  CHEMISTRY 


63 


proportion   of   the    dissolved   body    in    the    mother   liquor 
increases  until  finally  the    solute  also  comes  out  in  some 


MMtfnjt  Hoint< 


\ 
« 

/ 

1 

1 
1 

' 

F 

/ 

6<:,  per 

o<-nt.  C 

1000' 

, 

/ 

(CaM 

Iron) 

•* 

o 

'/ 

2 

/ 

/ 

7 

11:1 

y  <C  4-3 
1  \ 

ter  cent, 

c 

F 

L 

•c 

\ 

| 

\ 

\ 



._ 

1 

\ 

1 

cent.  C 

^ 

'\ 

\*.  — 

1.8  per  c 

ent  C^ 

\ 

^ 

hx 

$, 

\ 

\ 

\ 

Pearlite 

670^ 

8  per  ce 

V 

it.C 

Martens!!** 
(Steel  ) 

<rs 

\ 

\ 
\ 

,/ 

ought  1 

• 

„„ 

\ 

S85o. 

1 

x^ 

1600' 

Temperature 


Mi-It, n«  Poir 


FIG.  5 
C  =  Carbon  (Graphite  and  Diamond).    Fe  =  Iron  (a-  and  /3-  Ferrite) 

form  (for  example,  as  a  solid).  When  this  occurs,  the  low- 
est freezing  temperature  has  been  reached,  and  at  this 
temperature  the  rest  of  the  mass  assumes  a  solid  condition. 
This  mass  is  not  homogeneous ;  it  has  a  definite  composition, 


64  PHYSICAL  CHEMISTEY 

namely  that  peculiar  to  the  solution  at  the  lowest  tempera- 
ture of  freezing.  The  solid  solution  of  carbon  in  iron 
behaves  analogously.  The  carbon  content  of  the  solid  solu- 
tion increases  as  ferrite  is  deposited,  until  it  reaches  0.8  per 
cent.  From  this  the  carbon  now  begins  to  separate  at  670° 
in  the  form  of  cementite  (Fe3C).  In  the  case  of  solutions, 
the  complex  or  conglomerate  material,  produced  by  the  freez- 
ing of  the  solution  saturated  at  the  lowest  temperature  of 
freezing,  was  formerly  regarded  as  a  single  substance  on 
account  of  its  definite  composition.  In  the  case  of  aqueous 
solutions  it  was  named  a  cryohydrate.  The  same  thing  was 
done  in  the  present  case  and  the  product  was  called  pearlite. 
Its  true  nature,  however,  has  now  been  brought  to  light  in 
the  present  case  also,  and  the  constancy  of  its  composition 
is  explained.  It  is  a  complex  of  ferrite  and  cementite.  It 
corresponds  to  a  slowly  cooled  steel  containing  0.8  per  cent, 
of  carbon.  It  may  be  compared  with  special  aptness  to  the 
cryohydrate  of  a  salt,  which,  like  sulphate  of  copper,  occurs 
in  the  cryohydrate  in  the  form  of  a  true  hydrate.  In  this 
the  ice  corresponds  to  the  iron  and  the  hydrated  sulphate  of 
copper  to  the  carbide  of  iron.  Taking  a  cryohydrate  which 
solidifies  at  —5°,  we  may  express  the  analogy  diagram- 

matically  as  follows: 

-5° 
Cryohydrate  ^  Solution 

Ice  Hydrate 

and 

670° 
Pearlite  ±5  Solid  Solution 

Ferrite  Cementite 


INDUSTRIAL  CHEMISTRY  65 

All  the  phenomena  we  have  described  in  both  these  cases 
announce  themselves  in  precisely  the  same  manner  when  a 
thermometer  is  employed.  The  only  difference  is  that  in 
the  case  of  the  solution  the  progress  of  the  changes  can  be 
observed  with  the  eye,  while  in  the  case  of  iron  the  final 
investigation  of  the  structure  is  required  to  enable  us  to 
ascertain  that  when  0. 8  per  cent,  of  carbon  is  present  pearlite 
is  formed,  and  when  less  carbon  is  present  ferrite  and 
pearlite  are  found  together. 

What  will  happen  with  forms  of  iron  with  larger  propor- 
tions of  carbon  may  again  be  anticipated  by  comparison  with 
the  behavior  of  a  solution.  A  solution  which  contains  more 
sulphate  of  copper  than  corresponds  to  the  cryohydrate 
deposits,  when  cooling,  first  cupric  sulphate  and  then  the  cry- 
ohydrate. In  precisely  the  same  way  iron  with  a  higher 
proportion  of  carbon  gives  first  cementite  and  then  pearlite. 

That  this  analogy  is  supported  by  the  facts  to  so  great  an 
extent  is  due  to  an  entirely  unexpected  property  of  these 
solid  solutions  of  carbon  in  iron.  This  property  consists  in 
the  fact  that  in  spite  of  the  solid  condition  of  the  substance 
an  internal  separation  can  occur.  This  must  be  accompanied 
by  spatial  displacements  which  can  be  produced  only  by 
movement.  Internal  mobility  like  this,  however,  must 
become  less  with  diminished  temperature,  and  in  this  fact 
we  have  the  explanation  of  the  property  which  steel  has  of 
assuming  either  the  hard  or  the  soft  condition.  When  the 
cooling  is  rapid,  the  separation  we  have  just  mentioned  is 
passed  over,  and,  of  course,  does  not  take  place  in  the  mass 
once  it  becomes  cold.  The  solid  solution  remains  a  solid 


66  PHYSICAL  CHEMISTRY 

solution,  and  the  substance  is  in  this  case  hard  steel  (mar- 
tensite).  It  may  be  added  that  the  theory  of  solution  is  not 
entirely  unable  to  account  even  for  this  increase  in  the  hard- 
ness of  iron  when  carbon  is  contained  in  it  in  a  state  of 
solid  solution.  In  explanation  of  this  it  may  be  suggested 
that  a  dissolved  substance  lowers  the  vapor  tension  of  a  pure 
solvent,  and  therefore  in  solids  exerts  an  influence  against 
the  abrasion  of  the  surface.1  According  to  the  proportion  of 
carbon  these  solid  solutions  form  a  continuous  series  from 
the  soft,  pure  iron  to  the  very  hard  cementite. 

We  have  still  a  third  phenomenon  to  explain,  namely, 
the  well-known  separation  of  carbon  as  graphite,  which  fre- 
quently occurs  in  iron.  This  brings  us  back  to  the  forms  of 
the  substance  which  are  rich  in  carbon.  If  we  start  with 
cementite  (Fe3C),  which  corresponds  approximately  to  the 
white  cast  iron  of  industry,  we  find  that  a  separation  occurs 
in  this  compound  above  1000°.  From  it  graphite  and  a 
solid  solution  containing  1.8  per  cent,  of  carbon  are  pro- 
duced. This  temperature  and  this  particular  proportion 
of  carbon  thus  form  the  limits  for  those  kinds  of  iron 
which,  when  slowly  cooled,  produce  cementite.  We  can 
unite  this  point  (Fig.  5)  with  the  one  representing  0.8 
per  cent,  of  carbon  at  670°.  When  this  is  accomplished 
the  study  of  that  part  of  the  phenomena  which  is  con- 
nected with  the  transformation  of  a  solid  solution  is  almost 
exhausted. 

Let  us  now  turn  to  the  material  in  a  state  of  fusion,  that 
is  to  say,  to  the  liquid  solutions,  and  begin  with  pure  iron 

i  BABUS,  Wied.  Ann.,  Vol.  VII,  p.  383;  Vol.  XI,  p.  930. 


INDUSTRIAL  CHEMISTRY  67 

and  its  melting-point,  1600°.  This  point  we  place  on  the 
diagram  upon  the  horizontal  axis.  From  this  point  proceeds 
the  curve  of  melting  temperatures  as  they  are  depressed  by 
the  addition  of  carbon.  The  line  ends  at  the  iron  of  lowest 
melting-point,  which  contains  4.3  per  cent,  carbon  and  melts 
at  1130°.  In  consequence,  specimens  of  iron  containing 
more  carbon,  when  slowly  cooled,  deposit  even  at  tempera- 
tures above  1130°  the  excess  of  carbon  beyond  4.3  per  cent, 
which  they  contain.  From  the  fused  material  containing 
4.3  per  cent.,  as  Roozeboom  has  pointed  out  in  describing 
an  investigation  of  other  solid  solutions  and  the  fused  masses 
corresponding  to  them,  no  solid  solution  with  an  equal 
amount  of  carbon  is  formed.  The  solid  solution  contains 
only  2  per  cent.,  while  the  other  2.3  per  cent,  turns  into 
graphite  (under  high  pressures,  diamond).  This  point  is  the 
termination  of  the  series  of  solid  solutions  which  begin  at 
1000°  with  1.8  per  cent,  carbon,  and  when  slowly  cooled 
deposit  graphite.  In  the  diagram  these  two  points  are  thus 
connected  by  a  line. 

Finally  it  must  be  added  that  in  the  melted  material  also 
separation  may  fail  to  occur  when  the  cooling  is  rapid,  and 
so  from  a  melted  substance  having,  for  example,  the  composi- 
tion Fe3C,  cementite  in  large  leaf -like  crystals,  that  is  to  say, 
white  cast  iron,  may  be  obtained.  On  the  other  hand,  when 
the  cooling  is  slower,  graphite  will  first  appear,  then  cementite, 
and  finally  pearlite,  and  the  resulting  mixture  is  gray  cast 
iron.  The  diagram  thus  represents  the  stable  conditions 
which  are  reached  when  the  cooling  is  slow. 

If  we  now  turn  to  the  diagram  for  answer  to  definite 


68  PHYSICAL  CHEMISTRY 

questions  we  find  that  it  is  sufficient  simply  to  place  upon  it 
the  initial  condition  as  defined  by  the  percentage  of  carbon 
and  the  temperature.  The  phenomena  which  will  appear  as 
the  mass  cools  may  then  be  traced  by  going  horizontally  to 
the  left  until  one  of  the  lines  is  encountered.  This  line  will 
indicate  a  separation  of  some  definite  nature  during  which 
we  follow  the  direction  of  the  line  itself.  Rapid  cooling, 
on  the  other  hand,  corresponds  to  an  uninterrupted  move- 
ment to  the  left.  It  probably  will  be  most  interesting  to 
trace  the  behavior  of  a  mixture  of  6§  per  cent,  carbon  with 
93  J  per  cent,  iron  (corresponding  to  Fe3C),  beginning  at 
2000°  (that  is  to  say,  starting  from  the  melted  condition), 
and  noting  the  result  of  each  kind  of  treatment.  If  the 
cooling  is  rapid  cementite  is  formed.  If  the  cooling  is 
slower,  carbon  in  the  form  of  graphite  is  first  to  be  expected. 
The  amount  of  this  can  be  calculated,  since  iron  at  1130° 
containing  2  per  cent,  of  carbon  will  remain,  and  this  in  turn 
in  passing  down  to  1000°  will  sustain  a  further  separation 
of  graphite  until  iron  with  1.8  per  cent,  of  carbon  remains. 
The  amount  of  graphite  separated  from  the  original  100 
parts  of  iron  is  obtained  by  calculation,  thus: 


The  remaining  95.04  parts  of  iron  containing  1.8  per  cent. 
of  carbon  now  deposit  x  parts  of  cementite  containing  93J 
per  cent,  of  iron,  until  at  670°  the  percentage  of  carbon  has 
sunk  to  0.8.  The  remainder  (95.04  —  x)  yields  pearlite  with 
99.2  per  cent,  of  iron.  Thus  the  93.3  parts  of  iron  are 
divided  as  follows: 


INDUSTRIAL  CHEMISTRY  69 


Solving  this  equation  we  find  x  =  16. 

Collecting  these  results  we  find  that  100  parts  of  the 
original  substance  (containing  6§  per  cent,  of  carbon)  yield 
when  slowly  cooled  approximately  five  parts  of  graphite,  16 
parts  of  cementite  (containing  6§  per  cent,  of  carbon),  and 
79  parts  of  pearlite  (with  0.8  per  cent,  of  carbon). 


PHYSICAL  CHEMISTRY  AND  PHYSIOLOGY 


LECTURE  VI 

PHYSICAL  CHEMISTRY  AND  PHYSIOLOGY 

The  Theory  of  Solutions  Based  upon  the  Extension  of  Avogadro's 
Principle  and  its  Importance  in  Physiology —  Osmotic  Pressure  and 
Osmotic  Phenomena  —  The  Experiments  of  de  Vries  with  Plant 
Cells — The  Work  of  Donders  and  Hamburger  with  Blood  Cor- 
puscles—The Experiment  of  Massart  with  the  Human  Eye  and 
with  Bacteria — Loeb's  Work  on  Artificial  Fertilization — The 
Measurement  of  Osmotic  Pressure — Observation  of  the  Freezing 
Points  for  Determining  Equality  of  Osmotic  Pressure  —  Specific 
Action  of  Ions  in  Physiology. 

IF  you  refer  to  our  program  you  will  find  that  it  was 
my  intention  next  to  devote  two  lectures  to  the  relation  of 
physical  chemistry  to  physiology. 

By  way  of  introduction  let  me  recall  the  statement  that 
the  recent  development  of  physical  chemistry  rests,  so  to 
speak,  upon  two  foundation  stones.  One  of  these  is  usually 
known  as  the  theory  of  solution,  and  depends  essentially 
upon  the  extension  of  Avogadro's  principle  to  solutions. 
The  other  is  the  application  of  thermodynamics,  and  especially 
of  the  Carnot-Clausius  principle,  to  chemical  problems. 

In  physiology  the  theor^  of  solutions  finds  particular 
and  indeed  almost  exclusive  application.  The  thermody- 
namics may  be  left  out  of  account.  That  this  theory  has 
assumed  special  significance  in  the  science  of  physiology 
is  principally  due  to  two  factors,  which  must  now  be  set 
forth. 

73 


74  PHYSICAL  CHEMISTRY 

As  we  have  already  mentioned,  the  new  application  of 
Avogadro's  law,  just  like  the  original  one,  applies  strictly  only 
to  the  condition  of  infinite  dilution.  Nevertheless,  its 
practical  application  to  gases  at  the  ordinary  pressure  and  to 
solutions  of  the  strength  known  as  deci-normal  may  be 
carried  out  without  serious  misgiving.  Now  it  is  a 
fortunate  circumstance  that  in  the  region  of  physiology  the 
processes  which  have  to  be  considered  all  take  place  in  just 
such  dilute  solutions. 

To  this  we  must  add  a  second  factor.  The  new  theory 
of  solution  finds  its  simplest  expression  in  application  to 
osmotic  pressure.  In  this  form  it  states  that,  when  the  con- 
jcentration  is  low,  at  equal  temperatures  and  concentrations 
I  osmotic  pressure  and  gaseous  pressure  are  equal,  and  that  they 
i  vary  according  to  the  simple  laws  of  gases.  Now  it  is  a  fortu- 
nate accident  that  this  very  osmotic  pressure,  which  has  recent- 
ly become  accessible  to  calculation  and  quantitative  study, 
plays  a  conspicuous  part  in  the  physiological  processes  both 
of  animals  and  of  plants.  Its  significance  has  become  more 
and  more  apparent  of  recent  years,  and  the  literature  of  the 
subject  has  already  become  very  comprehensive. 

The  words  of  Loeb,  uttered  a  few  years  ago  in  a  lecture 
on  "The  Physiological  Problems  of  Today,"  delivered  at 
Ithaca,  recur  to  my  mind  (p.  11).  I  recall  particularly  the 
final  reference  of  the  author  to  the  fact  that,  since  the  period 
immediately  following  the  discovery  of  the  law  of  the  con- 
servation of  energy,  the  outlook  for  progress  in  physiology 
has  never  -appeared  brighter  than  at  present.  For  opening 
up  this  prospect  the  theory  of  solutions  is  undoubtedly 


PHYSIOLOGY  75 


primarily  responsible.  Other  writers  have  since  then 
expressed  themselves  in  the  same  way.1 

I  may  add  also  that  just  as  the  relation  of  physical  chem- 
istry to  technical  chemistry  has  led  to  Goldschmidt's  series 
of  lectures  before  the  employees  of  the  Badische  Anilin-  und 
Sodafabrik,  so  its  relation  to  physiology  and  medicine  has 
produced  a  series  of  addresses  by  Cohen  before  the  physi- 
cians of  Amsterdam.  German  and  English  translations  of 
these  lectures  have  now  appeared.2 

As  regards  details,  I  shall  take  as  my  starting-point  a 
brief  survey  which  I  presented  in  1891,  on  an  occasion  simi- 
lar to  this,  in  Utrecht.  At  that  time  everything  was  still 
in  an  incipient  stage.  Even  then,  however,  the  investiga- 
tions of  de  Vries 3  on  the  growth  of  plants  were  of  funda- 
mental importance.  In  connection  with  this  the  mechanism 
of  the  extraordinary  tension  which  distinguishes  growing 
plants,  and  is  absent  in  withering  ones,  was  studied.  The 
question  is  one  of  absorption  of  water  in  the  former  case 
and  of  loss  of  water  in  the  latter.  This  function,  however, 
is  accomplished  by  means  of  a  definite  cell  constituent  or 
organ,  whose  work  may  best  be  observed  in  plants  which, 
like  tradescantia  discolor,  have  a  colored  cell  content. 
When  withering  is  artificially  produced  by  dipping  the  cell 

1  HAMBURGER,  De  physische  scheilkunde  in  hare  beteekenis  voor  de  geneeskundige 
wetenschappen,  Groningen,  1901.    See  also  His,  Die  Bedeutung  der  lonent heorie  fiir 
die  klinische  Medizin,  Tftbingen,  1901. 

2  COHEN,  Physical  Chemistry  for  Physicians  and  Biologists,  translated  by  Dr. 
MARTIN  H.  FISCHER.    New  York:  Henry  Holt  &  Co.,  1903.    The  significance  of  the 
determination  of  freezing-points  has  been  treated  also  by  ROSEMANN,  Die  Gefrier- 
punktsbestimmung  und  ihre  Bedeutung  filr  die  Biologic,  Greifswald,  1901. 

3  "Eine  Methode  zur  Analyse  der  Turgorkraft,"  Pringsheim's  Jahrb.,  Vol.  XIV. 


76  PHYSICAL  CHEMISTRY 

in  a  sufficiently  concentrated  salt  solution,  water  tends  to  be 
abstracted.  The  microscopic  investigation  shows  that  in 
each  cell  an  elastic  skin  with  colored  contents,  which  usually 
fills  the  whole  cell,  becomes  separated  from  the  cell  wall 
and  suspends  itself  like  a  sphere  in  the  interior.  On  the 
other  hand,  this  so-called  protoplast  expands  when  the  salt 
solution  is  replaced  by  water.  It  soon  fills  and  ultimately 
stretches  the  cell.  When  this  condition  arises  cell  division 
and  growth  become  possible.  Obviously,  substances  which 
attract  water,  like  sugar,  salts,  and  vegetable  acids,  must  exist, 
dissolved  in  this  protoplast,  and  indeed  their  presence  may 
be  demonstrated.  At  the  same  time,  and  this  is  essential 
for  a  behavior  such  as  we  have  described,  the  elastic  mem- 
brane must  permit  the  passage  of  water,  but  not  that  of 
the  substances  just  mentioned  which  are  dissolved  in  the 
cell  sap.  In  the  contrary  case,  these  substances  would  soon 
diffuse  out  and  the  protoplast  would  lose  its  ability  to  lend 
to  the  plant  this  tension  or  turgor  which  is  essential  for 
development. 

Here  we  encounter  the  so-called  semipermeable  mem- 
brane which  is  ideal  for  the  exhibition  of  an  osmotic 
phenomenon,  and  was  presently  used  by  de  Vries  for  the 

measurement   of  osmotic   forces.       It    appeared    that    two 

i 
different  solutions  which  exerted  the  same  osmotic  influence, 

upon  the  protoplast  possessed  the  same  osmotic  pressure. 
Ability  barely  to  separate  the  protoplast  from  the  cell  wall  was 
taken  as  an  indication  of  the  presence  of  this  tendency  in  equal 
degree.  Equality  was  considered  to  exist  when  in  some  of 
the  cells,  but  not  in  all,  the  separation  from  the  polyhedral 


PHYSIOLOGY  77 


cell  wall  could  just  be  observed  through  the  microscope. 
Thus  two  facts  were  ascertained.  The  first  was  that  the 
osmotic  pressure  of  the  cell  content,  or,  as  we  prefer  to  call 
it,  of  the  content  of  the  tonoplast,  brings  about  growth.  The 
second  was  that  plants  furnish  a  means  of  determining  when 
solutions  are  isotonic,  or,  in  other  words,  when  their  osmotic 
pressures  are  equal. 

A  second  series  of  experiments  dealing  with  the  animal 
organism  was  soon  ranged  alongside  of  those  connected 
with  plant  physiology.  It  was  carried  out  by  a  renowned 
physiologist,  Bonders,  in  association  with  Hamburger.1 
These  investigators  found  that  the  behavior  of  the  blood,  or 
more  exactly  of  the  red  blood  corpuscles,  is  closely  con- 
nected with  the  osmotic  pressure  of  the  surrounding  fluid. 
The  phenomena  observed  may  be  briefly  described.  The 
blood  is  first  defibrinated,  that  is  to  say,  a  part  of  the 
albumin,  which  disturbs  the  experiments  by  coagulation,  is 
removed.  The  remaining  fluid  still  contains  the  red  blood 
corpuscles  and  presents  the  appearance  of  a  red  liquid. 
When  this  is  placed  in  solutions,  like  that  of  sodium  chloride, 
of  varying  concentrations,  two  different  phenomena  may  be 
presented  according  as  the  concentration  is  great  or  small. 
In  the  dilute  solutions  the  blood  corpuscles  lose  their 
coloring  matter  and  are  thus  deprived  of  the  constituent 
which  is  essential  to  the  performance  of  their  specific  func- 
tion. In  concentrated  solutions  they  retain  the  coloring 
matter,  but  soon  sink  to  the  bottom  of  the  colorless  solution 
of  the  salt.  On  setting  out  to  determine  the  limiting  con- 

1  Onderzoekingen  gedaan  in  het  physiologisch  labaratorium  der  Utrechtsche 
Hoogeschool  (3),  Vol.  IX,  p.  26. 


78  PHYSICAL  CHEMISTRY 

centrations  for  various  dissolved  substances  one  would 
naturally  expect  that  some  specific  influence  of  the  dissolved 
body  would  be  responsible  for  this  action  upon  the  blood 
corpuscles.  It  was  therefore  a  matter  of  surprise  to  discover 
that  here  again  the  osmotic  pressure  was  the  sole  controlling 
factor,  and  that  the  concentration  correspondences,  ascer- 
tained with  this  material,  coincided  exactly  with  those 
brought  to  light  by  de  Vries'  experiments  with  plants. 

It  may  perhaps  be  permissible  to  refer  to  a  series  of  experi- 
ments of  an  entirely  different  nature,  or  at  least  undertaken 
with  an  entirely  different  object.  In  them  the  human  eye  was 
the  subject  of  experiments  made  by  Dr.  Massart1  in  Luttich. 
He  introduced  into  the  eye,  presumably  his  own,  harmless 
solutions  which  had  previously  been  warmed  to  the  tempera- 
ture of  the  body.  Under  these  circumstances  it  was  noted 
that  when  the  solution  was  diluted  beyond  a  certain  limit 
the  eye  did  its  best  to  increase  the  concentration  of  the 
solution  by  evaporation.  An  unconquerable  inclination  to 
keep  the  eye  open  OP  to  separate  the -eyelids  was  experi- 
enced. On  the  other  hand,  when  the  concentration  of  the 
solution  exceeded  a  certain  limit,  the  eye  shut  of  its  own 
accord.  ^Evaporation  was  prevented,  and  the  formation  of 
tears  brought  about  the  necessary  dilution.  Here  again 
the  limiting  concentration  for  bodies  of  the  most  dif- 
ferent nature  was  determined,  and  the  same  relation  was 
discovered  between  these  solutions  as  had  been  noticed 
before  in  the  experiments  with  red  blood  corpuscles  and 
plant  cells. 

l  Archives  de  biologic  Beiges,  Vol.  IX  (1889),  p.  J5. 


PHYSIOLOGY  „  79 


We  may  conclude  the  list  of  our  illustrations,  now  that 
we  have  included  in  it  experiments  with  the  highest  organ- 
ism, by  introducing  something  of  a  precisely  corresponding 
nature  in  the  case  of  the  very  simplest  forms  of  life.  The 
author1  just  mentioned  has  found  that  bacilli  and  infusoria 
are  also  sensitive  indicators  of  this  limiting  osmotic  pressure. 
The  bacilli  are  placed  under  a  cover-glass  on  the  stage  of  a 
microscope.  When  bouillon  is  offered  to  them  in  a  micro- 
scopic capillary  tube  they  move  into  it  as  soon  as  they  notice 
its  presence.  The  prepared  bouillon,  however,  contains  a  dis- 
solved substance  whose  concentration  is  varied  from  experi- 
ment to  experiment.  Some  organisms  like  polytoma  uvello 
are  not  diverted  by  this  from  moving  along  the  capillary,  but 
they  are  killed  sooner  or  later  according  as  the  concentra- 
tion exceeds  a  certain  limit  to  a  greater  or  less  extent. 
Other  organisms,  like  Bacillus  megatherium,  do  not  enter 
the  capillary  if  danger  of  destruction  threatens  them, 
but  remain  at  the  entrance  to  it.  As  the  result  of  experi- 
ments with  different  substances  a  series  of  isotonic  concen- 
trations just  like  the  preceding  ones  is  obtained. 

1  shall  not  further  occupy  your  time  with  illustrations  of 
this  kind.     I  merely  refer  to  the  fact  that  the  above  data, 
striking  as  they  are,  were  collected  more  than  ten  years  ago, 
and  that  in  the  intervening  period  similar  things  have  been 
discovered  in  increasing  numbers.     A  complete  account  of 
the  literature  of  the  subject  was  given  a  year  ago  by  Koeppe.2 

JSee  also  WLADIMIROF,  ArchivfUr  Hygiene,  Vol.  X  (1891),  p.  81. 

2  Physikalische  Chemie  in  der  Medicin.    See  also  COHEN,  Physical  Chemistry  for 
Physicians  and  Biologists. 


80  PHYSICAL  CHEMISTRY 

Since  then,  however,  our  interest  has  been  attracted  to  the 
same  subject  by  Loeb's  discovery1  that  osmotic  pressure 
can  partly  replace  the  act  of  fertilization  of  the  eggs  of  sea- 
urchins.  These  eggs,  which  are  laid  in  sea-water,  die  when 
they  remain  unfertilized.  They  begin  to  develop,  however, 
if  a  temporary  elevation  in  the  osmotic  pressure  of  the  sea- 
water  is  produced  by  the  addition  of  substances  of  the  most 
varying  characters,  such  as  magnesium  chloride,  potassium 
chloride,  sugar,  and  urea.  The  development,  more  par- 
ticularly the  cell  division,  proceeds  until  the  organism 
begins  to  have  powers  of  movement.  It  may  be  added  that 
the  discoverer,  as  might  have  been  expected,  thought  at  first 
that  a  specific  action  of  the  foreign  material  was  responsible 
for  the  effect.  This  conception  arose  when  chloride  of  mag- 
nesium was  the  only  substance  that  had  been  tried.  Later, 
however,  when  entirely  different  substances  were  found  to 
have  the  same  effect  the  osmotic  explanation  suggested 
itself.  I  may  add  also  that  this  discovery,  when  presented 
to  the  American  public  without  the  osmotic  conceptions  con- 
nected with  it,  made  such  an  impression  that  Loeb  was 
heralded  in  the  newspapers  as  the  discoverer  of  the  elixir  of 
life.  Loeb  was  himself  probably  the  first  to  protest  against 
these  statements,  but,  as  some  suggestion  of  truth  is 
generally  to  be  found  in  newspaper  articles,  so  here  the 
report  was  a  somewhat  exaggerated  expression  of  the 
entirely  unexpected  intrusion  upon  life  phenomena  which 

I  American  Journal  of  Physiology,  Vol.  Ill,  p.  434;  Vol.  IV,  pp.  178,  423.  I  may 
add  that  the  mechanism  of  fertilization,  as  this  was  explained  by  Boveri  at  the 
Hamburg  Naturforscherversammlung  (1901),  seems,  as  I  pointed  out  at  the  time,  to 
represent  in  many  ways  ao  osmotic  process  produced  by  coagulation  of  albumen. 


PHYSIOLOGY  81 


physical  —  in    this    case    especially    osmotic  —  action     had 
permitted. 

After  it  had  been  shown  in  so  many  different  ways  what 
a  fundamental  part  osmotic  pressure  plays  in  physiological 
functions  the  question  of  the  measurement  of  this  pressure 
became  a  pressing  one.  Unfortunately  osmotic  pressure  is 
susceptible  of  direct  measurement  only  with  difficulty.  We 
have  indeed  succeeded  in  a  few  cases,  particularly  in  conse- 
quence of  the  efforts  of  Pfeffer,  in  measuring  this  pressure 
directly.  Without  any  doubt  we  shall  some  day  be  able  to 
do  it  in  all  cases,  but  so  far  an  easily  applicable  method  has 
not  been  discovered.  Nevertheless,  this  want  can  be  almost 
entirely  supplied  in  consequence  of  the  relation  which  ther- 
modynamics shows  to  exist  between  osmotic  pressure  and  the 
depression  of  the  freezing-point.  This  relation  again  holds 
only  for  dilute  solutions.  We  know  that  solutions  freeze  at 
a  temperature  lower  than  the  solvent.  Thus  sea-water  freezes 
a  considerable  distance  below  0°.  We  may  even  predict  by 
calculation  that  a  solution  which  exhibits  an  osmotic  pressure 
of  one  atmosphere  at  0°  will  freeze  at  —0.084°.  The  two 
values  are  proportional  to  one  another  in  the  case  of  dilute 
solutions  such  as  exist  in  living  organisms.  It  would  be  hard 
to  find  any  other  region  in  which  several  different  branches  of 
science — in  this  case,  mathematics,  physics,^hemistry,  anat- 
omy, and  physiology — rhave  joined  hands  over  the  same 
problem.  Here  physiology  required  the  determination  of 
the  osmotic  pressure,  and  experimental  determinations  neces- 
sary for  its  theoretical  deduction  had  been  carried  out  by 
Raoult,  Eyckman,  Beckmann,  and  others.  In  any  case,  the 


82  PHYSICAL  CHEMISTRY 

absolute  dimensions  of  the  osmotic  pressure  do  not  usually 
require  to  be  known.  What  we  need  are  the  relative  values, 
which  are  given  directly  by  observation  of  the  depressions  of 
the  freezing-point.  Equality  in  osmotic  pressure,  which  is 
often  so  important  in  physiology,  may  be  inferred  directly 
from  identity  in  the  freezing-points. 

One  important  conclusion  from  these  investigations  is 
that  in  the  organism  as  a  whole  the  most  different  liquids 
must  be  in  osmotic  equilibrium  with  one  another  and  must 
therefore  possess  the  same*  freezing-point.  The  same  must 
be  true  of  the  more  complex  case  of  mother  and  child  before 
birth.  A  notable  exception  is  found  in  the  secretions  of  the 
kidneys,  which  may  sometimes  exhibit  abnormally  high 
osmotic  pressure.  Anomalies  of  this  kind  may  be  indicative 
of  diseases  of  the  kidneys  and  of  the  heart,  which  is  so  closely 
related  to  them  in  its  functions.  Again,  in  certain  cases, 
such  as,  for  example,  when  one  kidney  is  to  be  removed,  the 
normal  behavior  of  the  other  can  be  determined  in  advance 
by  freezing-point  measurements.1 

It  would  not  be  advisable  for  me  to  linger  any  longer  in 

this  entirely  foreign  territory.     I  turn,  therefore,  to  another 

conception  still  related  to  physiology  which  has  been  sug- 

gested by  the  co-operation  of  physical  chemistry.     This  is 

connected  with  electrolytes. 

As  we  have  already  had  occasion  to  mention,  tne  new  con- 
ception of  solutions,  and  especially  of  dilute  solutions,  forces 
us  to  the  belief  that  in  electrolytes  an  actual  splitting  of  the 
dissolved  srfbstance  has  occurred.  Such  are  the  solutions  of 


,  loc.  cit.;  GALEOTTI,  "Ueber  die  Arbeit  welche  die  Nieren  leisten," 
Ar'chivf.  Anat.  und  PhysioL  (1902),  p.  200. 


PHYSIOLOGY  83 


acids,  bases,  and,  particularly,  salts.  The  dissociation  leads 
to  the  formation  of  so-called  ions  which  are  liberated  during 
electrolysis.  In  this  way  chloride  of  sodium,  for  example,  is 
held  to  contain  in  its  solution  positively  charged  sodium  and 
negatively  charged  chlorine.  The  physical  properties  are 
in  harmony  with  this  theory,  and  indeed  render  it  almost 
inevitable,  since  the  osmotic  pressure  has  nearly  double  its 
normal  value.  The  most  various  chemical  properties  are  also 
explicable  by  this  assumption  and  by  it  alone.  And  now  the 
territory  of  physiology  is  being  scanned  in  many  directions 
from  the  same  point  of  view.  As  time  presses  I  must 
close  with  a  few  mere  hints  of  what  is  being  done.  I  call 
your  attention  particularly  to  the  fact  that  the  activity  of  a 
salt  toward  an  organism  may  depend  upon  three  factors. 
Those  are  the  two  ions  and  the  salt  itself.  Even  the  latter  may 
be  present  in  the  organism,  since  the  dilution  is  a  limited 
one.  Osmotically  the  ions  and  molecules  behave  alike,  and 
the  actions  involving  withdrawal  of  water  must  be  considered 
in  the  light  of  this  fact.  Specific  actions,  however,  are  per- 
ceptible and  we  naturally  attribute  the  similar  behavior  of 
different  salts  in  this  respect  to  the  presence  of  the  same  ion 
in  each.  Thus  we  explain  the  poisonous  influence  of  mer- 
cury salts  to  the  mercury  ion.  In  this  direction  important 
conclusions  have  already  been  reached.1  For  example,  not 
all  mercury  compounds  contain  the  ion  in  question,  but  in 
precisely  these  cases  the  poisonous  property  is  absent.  The 
toxic  effect  varies  also  from  case  to  case  according  to  the 
degree  of  ionization. 

1  PAUL,  Hamburger  Naturforscherversammlung,  1901. 


LECTUKE  VII 

PHYSICAL  CHEMISTRY  AND  PHYSIOLOGY 

Enzymes,  Their  Preparation  and  Nature  —  Enzymes  as  Catalytic 
Agents — Chemical  Equilibrium  —  Graphic  Representation  of  In- 
complete Chemical  Interactions  — Incomplete  Actions  Occur  When 
Heat  Change  is  Small — Application  to  the  Behavior  of  Enzymes — 
Illustrations — The  Synthesis  of  Amygdalin. 

THIS  second  lecture  on  physical  chemistry  in  its  relation 
to  physiology  will  be  devoted  to  the  consideration  of  the 
behavior  of  enzymes.  As  we  all  know,  this  name  has  been 
given  to  certain  exceedingly  complicated  compounds  which 
are  found  in  animal  and  vegetable  organisms.  They  have 
the  property  of  producing  chemical  changes  without  being 
themselves  altered  in  the  process,  and  they  bring  about  such 
changes  in  quantities  of  other  bodies  which  are  altogether 
out  of  proportion  to  their  own  amount.  One  of  the  oldest 
examples  is  furnished  by  the  substance  emulsin,  which  is  con- 
tained in  almonds.  Wohler  found  that  it  had  the  power  to 
decompose  amygdalin,  which  is  found  along  with  it,  and  is 
otherwise  a  stable  body.  The  products  of  this  decomposition 
are  glucose,  benzaldehyde,  and  hydrocyanic  acid. 

An  example  from  more  recent  work  may  be  placed  along- 
side of  this.  As  we  know,  sugar,  or  rather  a  special  kind  of 
sugar  known  as  glucose,  is  decomposed  by  yeast  into  alcohol 
and  carbon  dioxide.  This  is  in  fact  the  alcoholic  fermenta- 
tion which  is  used  in  the  preparation  of  spirituous  liquors. 
Until  a  few  years  ago  this  transformation  was  considered  to 

84 


PHYSIOLOGY  85 


be  one  of  the  life  processes  of  yeast.  This  is  one  of  the 
lower  organisms  and  seemed  to  develop  in  the  course  of  fer- 
mentation by  consumption  of  sugar  and  production  of  carbon 
dioxide  and  alcohol.  Recently,  however,  Buchner  has 
shown  that  this  influence  of  yeast  can  take  place  without 
the  presence  of  the  living  organism.  If  the  yeast  is  killed 
by  warming  to  a  definite  temperature,  a  substance  may  be 
extracted  from  it  which  can  still  produce  fermentation, 
although  it  possesses  neither  life  nor  organized  form.  This 
substance  is  called  zyma.se,  and  when  its  solution  is  mixed 
with  glucose  the  effervescence  resulting  from  the  evolution 
of  carbon  dioxide  and  the  accompanying  production  of 
alcohol  occur  in  the  normal  manner. 

The  known  enzymes  are  now  very  numerous,  and,  what  is 
more  important,  it  appears  as  if  all  fermentations  were  pro- 
duced by  bodies  of  this  class.  This  is  important  on  account 
of  the  physiological  significance  of  the  fact  that  what  was 
formerly  supposed  to  be  due  primarily  to  the  necessary 
presence  of  a  living  organism  is  now  found  to  be  produced 
by  unorganized  substances.  It  still  remains  true,  however, 
that  animals  and  plants  are  concerned  in  the  formation  of 
these  substances.  The  moment,  however,  that  these  actions 
of  enzymes  were  found  to  occur  without  the  direct  interven- 
tion of  life,  the  changes  became  classifiable  as  catalytic 
actions.  These  changes  must  indeed  be  regarded  as  com- 
plicated, when  we  consider  the  nature  of  the  enzyme  and  its 
mode  of  action.  They  are  widely  separated  in  this  respect 
from  the  actions  of  platinum  sponge,  by  the  help  of  which, 
for  example,  water  is  produced  from  its  elements.  In  spite 


86  PHYSICAL  CHEMISTRY 

of  this,  however,  physical  chemistry  is  in  a  position  to  make 
some  suggestions,  since  some  of  the  conclusions  to  which  it 
points  may  be  applied  irrespective  of  the  mechanism  of  the 
change  involved.  The  effective  range  of  these  suggestions 
is  not  at  all  diminished  by  complexity  in  the  nature  of  the 
action.  In  treating  the  subject  from  this  point  of  view, 
therefore,  the  composition  and  chemical  character  of  enzymes 
do  not  require  to  be  considered  in  detail.  They  seem  to  be 
most  nearly  allied  to  the  albumins.  We  may  hope  that  an 
exact  study  of  their  internal  structure  will  some  day  be  able 
to  explain  their  remarkable  specific  actions.  It  will  explain, 
for  example,  precisely  why  one  enzyme  acts  upon  glucose, 
while  another  acts  upon  amygdalin.  For  the  present,  how- 
ever, we  approach  the  subject  from  an  entirely  different  point, 
and  regard  the  enzymes  simply  as  bodies  which  produce  or 
hasten  chemical  reactions  without  ultimately  themselves  suf- 
fering any  change.  It  may  be  that  they  do  undergo  changes 
of  a  transitory  kind,  and  that,  to. give  a  simple  illustration, 
the  enzyme  combines  with  the  original  body  and  then  gives 
off  decomposition  products  in  such  a  way  that  it  is  ultimately 
regenerated..  Still,  consideration  of  these  details,  as  we  have 
said,  is  not  essential,  and  provided  the  enzyme  is  ultimately 
recovered  unaltered,  the  principles  of  which  we  are  about  to 
speak  are  applicable. 

These  principles  depend  upon  chemical  equilibrium.  We 
have  already  mentioned  this  subject  several  times.  I  recall 
to  your  mind  the  fact  that  some  chemical  reactions,  includ- 
ing the  best-known  ones,  such  as  the  formation  of  water  from 
its  elements,  proceed  to  completion.  In  the  case  cited,  for 


PHYSIOLOGY  87 


example,  the  explosive  gas  undergoes  complete  transforma- 
tion. Nevertheless,  this  sort  of  change  is  by  no  means  gen- 
eral, but  quite  the  contrary.  I  take,  for  example,  the  action 
of  an  acid,  such  as  acetic  acid,  upon  ethyl  alcohol.  This 
proceeds  slowly  at  the  ordinary  temperature,  and  more  rapidly 
when  heat  is  applied,  and  yields  finally  ethyl  acetate  and  water. 

C2H402  +  C2H60  =  C2H302  .  C2H5  +  H2O 

The  essential  point,  however,  as  was  shown  by  Berthelot  and 
Pe"an  de  St.  Gilles,  is  that  this  change  does  not  proceed  to 
complete  consumption  of  the  constituents.  On  the  contrary, 
the  change  ceases  when  two-thirds  of  the  material  has  been 
transformed.  Thus,  if  we  take  60  g.  of  acetic  acid  and  46  g. 
of  alcohol,  only  59  g.  of  ethyl  acetate  are  formed,  instead  of 
the  theoretical  amount  (88  g.).  As  we  all  know,  the  explana- 
tion lies  in  the  fact  that  water  and  ethyl  acetate  act  upon 
one  another  to  produce  the  reverse  change.  A  similarly 
limited  action  also  takes  place  when  we  start  with  88  g.  of 
ethyl  acetate  and  18  g.  of  water.  The  condition  of  seeming 
rest  which  is  finally  reached  is  the  result,  therefore,  of  two 
opposite  reactions  which  were  proceeding  with  equal  speed, 
and  are  represented  by  the  expression: 

C2H402  +  C2H60  ±5  C2H302  .  C2H5  +  H2O . 

This  presents  the  final  condition  and  gives  also  the  relative 
proportions  of  the  materials. 

It  may  perhaps  be  well  to  put  this  concretely  in  still 
another  form.  Let  us  imagine  that  the  change  in  composi- 
tion from  left  to  right  is  represented  in  Fig.  6  in  such  a  way 
that  A  is  the  mixture  of  acid  and  alcohol,  and  B  that  of  ester 


88 


PHYSICAL  CHEMISTRY 


FIG.  6 


and  water.  Then,  at  the  point  C,  two-thirds  of  the  distance 
from  A,  is  shown  the  final  condition  of  both  systems  when 
equilibrium  is  reached.  Let  now  the  chemical  change  be 
represented  by  a  rolling  ball,  which  proceeds  along  the  line 
DEF  and  comes  to  rest  at  the  lowest  point  E.  .The  forma- 
tion of  ester  now  corresponds 
to  the  motion  along  DE,  the 
reverse  action,  the  saponifica- 
H  tion,  to  that  along  FE.  In 
P  order  to  enable  the  figure 
K  more  closely  to  represent  the 
facts,  we  must  suppose  further 
,  that  the  ball  has  no  inertia, 
and  that  therefore  it  does  not 
reach  the  point  E  with  its  maximum  velocity  and  proceed 
beyond  it,  but  that  it  gradually  moves  more  and  more  slowly 
until  it  comes  to  rest  at  this  point. 

In  this  diagram  we  may  place  also  the  reactions  which 
appear  to  be  complete,  for  it  has  gradually  come  to  be  seen 
that  even  in  their  case  a  limit  is  reached.  Only  this  limit 
lies,  as  we  might  represent  it  by  the  curve  GH,  so  far  to  one 
side  that  the  most  delicate  means  of  investigation  are  required 
to  show  that  the  change  has  been  in  reality  partial  at  all. 
Our  conceptions  have  in  fact  fundamentally  changed  in 
respect  to  these  matters.  Formerly  cases  of  chemical 
equilibrium  appeared  to  be  exceptional.  Now  we  have 
every  reason  to  think  that,  at  least  where  homogeneous 
mixtures  of  the  systems  under  transformation  are  in  ques- 
tion, as  is  the  case  in  solutions,  the  attainment  of  equilib- 


PHYSIOLOGY  89 


rium  is  invariable,  and  complete  change  is  to  be  considered 
as  only  apparent. 

We  may  now  proceed  a  step  farther,  however.  We  can 
perceive  a  means  of  predicting  which  actions  will  proceed  in 
such  a  way  that  the  existence  of  a  limit  will  not  be  percep- 
tible at  ordinary  temperatures,  and  will  become  noticeable 
only  when,  at  higher  temperatures,  the  limit  has  been  dis- 
placed toward  the  middle.  Such  reactions  must  be  those 
which  are  accompanied  by  a  great  development  of  heat.  In 
this  we  encounter  once  more  the  principle  of  maximum  work 
(p.  31)  in  a  somewhat  changed  form.  To  this  class  belong, 
for  example,  those  changes  which  are  accompanied  by  com- 
bustion or  explosion. 

The  state  of  affairs  is  quite  different  when  the  develop- 
ment of  heat  is  small,  and  the  existence  of  a  large  group  of 
cases  in  which  the  heat  development  is  actually  zero  at  all 
temperatures  is  very  striking.  These  reactions  are  some- 
what out  of  the  ordinary  line.  They  are  those  in  which 
optically  active  substances,  which  have  the  power  of  rotating 
the  plane  of  polarized  light,  are  turned  into  bodies  of 
exactly  the  same  composition  with  precisely  the  opposite 
optical  action.  Thus  ordinary  (dextro-)  tartaric  acid  may  be 
changed  into  Isevo-tartaric  acid,  a  substance  having  the  same 
composition,  whose  structure,  however,  is  a  mirror-image  of 
that  of  the  former.  Here  the  heat  developed  by  the  change 
is  absolutely  zero,  as  we  should  expect  from  the  identity  of 
the  internal  dimensions  of  both  molecules.  In  correspond- 
ence with  this,  the  position  of  equilibrium  lies  exactly  half 
way  between  the  two  kinds,  and  leans  therefore  neither  to 


90  PHYSICAL  CHEMISTRY 

the  side  of  the  dextro-  nor  to  that  of  the  laevo-acid.  It 
produces  an  inactive  mixture  of  the  two  in  precisely  equal 
proportions.  This  state  of  affairs  may  thus  be  represented 
(Fig.  6)  by  the  symmetrical  curve  IK,  with  the  ball  at  the 
lowest  position  L. 

Let  us  now  return  to  the  action  of  enzymes  and  note  the 
prominent  fact  that  the  chemical  changes  which  they  bring 
about  are  invariably  such  as  are  accompanied  by  small 
developments  of  heat.  Thus,  the  modification  which  butter 
undergoes  when  it  becomes  rancid  is  a  reaction  whose  heat 
change  is  almost  zero.  From  this  it  follows  almost  of  neces- 
sity that  an  easily  observable  state  of  equilibrium  must  be 
reached,  although  the  question  might  be  asked  whether, 
since  a  strange  agent  like  an  enzyme  is  concerned,  complete 
change  would  not  after  all  occur.  To  this  question  our 
diagram  (Fig.  6)  gives  a  decisive  answer.  Such  a  displace- 
ment of  the  equilibrium  would  correspond  to  the  movement 
of  the  ball  upward  from  the  lowest  position,  and  would  rep- 
resent therefore  an  accomplishment  of  work.  This,  however, 
is  excluded  if  the  enzyme  acts  as  a  catalyzer,  and  is  found 
unchanged  at  the  end.  Even  if  we  assume  a  slight  change 
or  weakening  of  the  enzyme,  the  reply  is  not  materially 
affected,  since  this  would  bring  about  nothing  more  than  a 
slight  accomplishment  of  work,  and  therefore  a  slight  dis- 
placement of  the  equilibrium. 

Having  reached  this  point,  we  are  now  forced  to  accept  a 
surprising  conclusion  in  regard  to  the  influence  of  enzymes. 
If  these  are  not  in  a  position  to  displace  the  equilibrium 
point,  and  this  equilibrium  point  is  noticeably  divergent 


PHYSIOLOGY  91 


from  the  condition  of  completed  action,  it  follows  of  neces- 
sity that  when  a  certain  change  can  be  produced  or  hastened 
the  opposite  change  must  be  influenced  in  precisely  the 
same  way.  Some  confirmations  of  this  conclusion  are 
already  known.  Thus  Lemoine  found  that  the  formation  of 
hydrogen  iodide  from  hydrogen  and  iodine  is  hastened  by 
platinum  sponge,  and  that  this  foreign  body  is  not  affected 
by  the  change.  This  being  the  case,  the  limit  of  the  change, 
which  is  reached  long  before  complete  union  has  occurred, 
is  not  affected  by  the  platinum.  The  expectation  that  plati- 
num would  hasten  the  decomposition  of  hydrogen  iodide, 
which  follows  necessarily  from  these  facts,  was  confirmed  by 
experiment.  Again,  quite  recently,  Brereton  Baker  has 
found  that  perfectly  dry  ammonium  chloride  is  volatile 
without  decomposition  and  that  perfectly  dry  hydrogen 
chloride  does  not  combine  with  ammonia  to  form  ammonium 
chloride.  A  trace  of  moisture,  however,  which  instantly 
leads  to  the  formation  of  ammonium  chloride  from  its  con- 
stituents in  the  cold,  assists  the  opposite  reaction  in  pre- 
cisely the  same  way  and  produces  decomposition  at  a  high 
temperature. 

In  the  case  of  enzymes  the  situation  is  certainly  less 
simple,  since,  with  the  complex  organic  compounds  which 
are  concerned,  so  many  different  kinds  of  reaction  are  pos- 
sible. Thus  instead  of  the  reverse  action  a  quite  different 
one  might  occur.  If  this  possibility  were  excluded  we 
might  state  as  a  generalization  that  the  enzymes  must  have 
the  capacity  to  build  up  from  their  parts  those  bodies  which 
they  have  the  power  to  decompose  into  the  same  constitu- 


92  PHYSICAL  CHEMISTEY 

ents.  If  this  were  true,  a  very  simple  means  would  be 
furnished  for  the  synthesis  of  physiological  substances  of 
the  very  highest  interest.  Thus,  since  the  albumins  under 
the  influence  of  ferments  like  trypsin  are  decomposed  into 
simpler  compounds,  we  should  see  a  prospect  of  reconstruct- 
ing them,  with  the  help  of  trypsin,  from  the  same  products 
of  decomposition. 

Let  us  now  turn  to  what  has  actually  been  done  in  this 
direction.  The  first  realization  of  what  has  been  hinted  at 
above  seemed  to  have  been  achieved  by  Hill,  when,  as  a  result 
of  his  work  on  reversible  hydrolysis,1  he  found  that  maltose, 
which  contains  twelve  carbon  atoms  in  the  molecule  and 
can  be  split  by  an  enzyme  contained  in  yeast,  with  forma- 
tion of  glucose: 


could  be  reconstructed  from  glucose  by  the  help  of  the  same 
enzyme.  Unfortunately  it  was  discovered  later  that  the 
form  of  sugar  produced  by  this  reversal  is  not  maltose,  but, 
at  all  events  for  the  most  part,  the  isomeric  isomaltose.2 
The  synthetic  powers  of  the  enzymes  have  not  been  discred- 
ited by  this,  however,  for  the  very  latest  discovery  of 
Emmerling3  has  come  to  the  rescue.  He  has  shown  that 
amygdalin,  which  is  decomposed  by  emulsin  into  glucose, 
benzaldehyde,  and  hydrocyanic  acid, 

C20H27NOU  +  2H20  =  2C6H1206  +  C7HeO  +  HNC  , 


1  Jour.  Chem.  Soc.,  Vol.  LXXIII  (1898),  p.  634;  Ber.  d.  deutsch.  chem.  Gesell.,  Vol. 
XXXIV,  p.  1380. 

2  EMMERLING,  Ber.  d.  deutsch.  chem.  Gesell.,  Vol.  XXXIV,  pp.  600,  2206. 

.,  p.  3810. 


PHYSIOLOGY  93 


can  be  reconstructed  from  the  glucoside  of  mandelic  nitrile 
and  glucose  by  means  of  the  yeast  maltase,  which  Hill  had 
also  employed: 

CUH17N06  +  C6H1206  =  C20H27NOn  +  H3O . 

Although  obviously  in  this  direction  only  a  few  pre- 
liminary steps  have  yet  been  taken,  it  cannot  be  doubted 
that  these  discoveries  will  lead  to  an  exceedingly  rich  field 
of  work.  They  may  possibly  conduct  synthetic  organic 
chemistry  to  the  solution  of  the  highest  problems.  It  is  to 
be  hoped  that  they  will  do  so,  not  only  because  unsuspected 
possibilities  for  the  construction  of  those  substances  which 
play  so  important  a  part  in  living  organisms  is  offered,  but 
also  because  the  methods  which  are  involved  approach  much 
more  nearly  the  natural  modes  in  which  the  substances  in 
question  are  formed  than  do  our  ordinary  syntheses.  Indeed, 
these  methods  may  actually  be  the  natural  ones. 


PHYSICAL  CHEMISTKY  AND  GEOLOGY 


/ 


LECTURE  VIII 

PHYSICAL  CHEMISTRY  AND  GEOLOGY 

The  Formation  and  Structure  of  Geological  Salt  Deposits  —  Early 
Study  of  Deposition  from  Solutions  Containing  Several  Salts,  by 
Usiglio  —  The  Proportion  of  the  Constituents  as  Well  as  Their 
Solubility  to  be  Considered  —  The  Modern  Method  of  Study  and 
Graphic  Representation — The  Case  of  a  Single  Salt  and  Water  at 
a  Fixed  Temperature,  25° — The  Case  of  Two  Salts  Simultaneously 
Present  at  25°— The  Case  of  Three  Salts  at  25°— The  Problem  of 
Sea-Water  at  25°,  with  All  Salts  Present. 

I  SHALL  devote  the  last  two  lectures  to  the  relation  of 
chemistry  to  geology,  and  in  doing  so  shall  bring  together 
the  results  of  investigations  which  I  have  made  during  the 
last  few  years,  for  the  most  part  in  association  with  Meyer- 
hoffer.1 

We  may  say  in  a  general  way  that  in  the  formation  of  the 
crust  of  the  earth  two  processes  falling  within  the  territory 
of  physical  chemistry  have  played  an  important  part: 

1.  The  cooling  and  gradual  solidification  of  masses  origi- 
nally fluid. 

2.  The  drying  up  of  originally  liquid  solutions,  accom- 
panied similarly  by  the  gradual  formation  of  solid  deposits. 

In  both  cases  displacements  of  conditions  of  equilibrium 
are  concerned.  These  are  partly  of  a  physical  nature,  such 
as  gradual  solidification  and  crystallization,  and  partly  con- 
sist in  displacements  of  chemical  equilibria  under  the  influence 
of  changes  in  concentration  and  temperature. 

iSitzungsber.  der  kdnigl.  preuss.  Akad.  der  Wissensch.,  von  1897  an. 

97 


98  PHYSICAL  CHEMISTRY 

By  way  of  reaching  speedily  the  subject  which  is  to 
concern  us,  it  must  be  stated  that  the  great  processes  of 
evaporation  which  are  of  geological  importance  have  taken 
place  in  sea-water,  or  at  least  in  a  salt  solution  having  a 
composition  closely  approaching  that  of  the  sea.  This 
process  is  primarily  responsible  for  the  formation  of  the 
great  salt  deposits  which  now  constitute  the  most  important 
commercial  source  of  common  salt.  If  rock  salt  or  sodium 
chloride  were  alone  concerned,  and  sea-water  contained  no 
other  substances,  the  problem  of  evaporation  would  hardly 
require  any  explanation.  The  water  would  leave  and  the 
salt  "^vould  remain  behind.  The  fact  of  chief  importance 
technically,  as  well  as  mineralogically  and  geologically,  is  that 
the  subordinate  constituents  of  sea-water  have  to  be  con- 
sidered. These  are  such  substances  as  magnesium,  potassium, 
and  calcium  in  the  form  of  chlorides  and  sulphates,  as  well 
as  boric  acid,  carbonic  acid,  bromine,  iron,  and  so  forth. 
During  the  process  of  evaporation  these  substances  accumu- 
lated for  the  most  part  in  the  mother-liquor  until,  as  at 
Stassfurt,  they  ultimately  formed  a  mineral  layer  on  the  top 
of  the  rock  salt.  They  were  originally  set  aside  as  value- 
less, and  were  classed  by  the  miners  as  stripping.  Now 
they  have  acquired  a  technical  importance  which  far 
exceeds  that  of  the  rock  salt  lying  below  them,  and  the 
mode  of  formation  of  some  thirty  minerals,  some  in,  some 
over,  and  some  under  the  common  salt,  presents  a  prob- 
lem whose  solution  could  not  be  approached  until  very 
recently.  We  have  in  fact  only  lately  come  into  possession 
of  adequate  means  of  attacking  the  problem  and  of 


GEOLOGY  99 


thoroughly  comprehending  tho  law  describing  the  deposition 
of  materials  from  complex  solutions. 

By  way  of  giving  some  insight  into  the  situation,  it 
should  be  mentioned  that  the  stratified  deposits,  as  we  study 
them  from  the  bottom  upwards,  may  be  divided  into  four 
main  regions.  The  first  two  are  named  in  order  after  two 
compounds  of  calcium  which  are  contained  in  them. 
They  are  the  anhydrite  (CaSOJ  and  the  polyhalite  (2CaSO4 . 
MgSO4  .  K2SO4  .  2H2O)  regions.  In  both  of  these  rock 
salt  alternates  regularly  with  thin  layers,  in  the  first  of  anhy- 
drite and  in  the  second  of  polyhalite.  These  are  commonly 
regarded  as  marking  years,  and  their  formation  is  supposed 
to  be  connected  with  the  seasons.  The  two  upper  regions 
are  named  after  prominent  magnesium  compounds  which  are 
contained  in  them,  namely,  kieserite  (MgSO4  .  H2O)  and 
carnallite  (MgKCl3  .  6H3O).  Eock  salt  is  a  uniform  com- 
panion of  these  substances,  although  it  is  present  in 
constantly  diminishing  proportions.  This  rather  regular 
system  of  deposits  is  usually  regarded  as  the  product  of 
direct  evaporation  of  a  salt  solution  similar  to  sea-water,  and 
is  therefore  designated  as  primary.  Certain  other  products 
are  secondary  and  have  been  formed  from  the  above  by  sub- 
sequent change,  and  especially  by  the  action  of  water.  Thus 
sylvite  (KC1)  was  formed  from  carnallite,  and  kainite 
(MgSO4  .  KC1 .  3H2O)  from  the  latter  and  kieserite. 

This  conception  of  the  relations  of  the  substances  was 
first  subjected  to  experimental  investigation  by  the  Italian 
chemist  Usiglio.1  He  evaporated  sea-water  on  a  large  scale 

1  Ann.  de  Chim.  et  de  Phys.  (8>,  Vol.  XXVII  (1849),  pp.  92, 172. 


100  PHYSICAL  CHEMISTRY 

and  obtained  as  deposits  calcium  carbonate,  sodium  chloride, 
gypsum  (CaSO4  .  2H2O),  magnesium  sulphate  with  seven 
and  with  six  molecules  of  water  of  crystallization,  schonite 
(MgSO4  .  K3SO4  .  6H2O),  potassium  chloride,  carnallite, 
and  magnesium  chloride.  Some  very  important  constituents 
of  the  mineral  deposits,  and  especially  anhydrite,  polyhalite 
and  kieserite,  which  lend  their  names  to  three  of  the  four 
regions,  were  lacking.  We  shall  presently  learn  why  experi- 
ments like  those  of  Usiglio  fail  to  correspond  completely 
with  the  natural  processes.  It  was  necessary,  therefore,  to 
take  up  the  problem  by  a  different  method  and  in  a  more  gen- 
eral manner,  and  to  secure  an  answer  to  the  question,  What 
is  the  influence,  not  only  of  the  composition  of  the  solution, 
but  also  of  temperature,  pressure,  and  time  on  the  nature  of 
the  deposits  which  are  formed  ?  We  have  only  recently  been 
able  successfully  to  attack  this  question  and  to  answer  it. 

I  must  first  give  prominence  to  the  fact  that  one  fre- 
quently stated  and  indeed  seemingly  obvious  principle  is 
nevertheless  not  strictly  correct.  This  principle  is  to  the 
effect  that  the  order  in  which  deposits  appear  must  correspond 
to  the  order  of  solubility  in  such  a  manner  that  the  most  sol- 
uble substance  must  come  out  last.  It  is  certainly  true  that 
taken  as  a  whole  the  order  of  the  natural  deposits  is  in  har- 
mony with  this,  and  that  first  a  slightly  soluble  calcium  salt 
appears  in  the  form  of  anhydrite,  then  its  combinations  with 
more  soluble  sulphates,  as  polyhalite,  then  the  easily  soluble 
magnesium  sulphate  by  itself  as  kieserite,  and  finally  the 
very  soluble  carnallite.  Yet  it  would  obviously  be  quite 
possible  to  produce  a  solution  so  rich  in  magnesium  sulphate 


GEOLOGY  101 


and  so  poor  in  gypsum  that  when  it  was  concentrated  the 
more  soluble  magnesium  sulphate  would  appear  first.  Thus 
the  composition  of  the  solution  plays  an  important  part  in 
the  order  of  the  deposits.  Then,  too,  while  the  solubility  is 
also  a  determining  factor,  we  have  to  remember  that  it  may 

<: - — • 

vary  very  widely  under  the  influence  of  other  bodies  which 
are  simultaneously  present. 

Let  us  first  consider  these  two  factors,  the  composition  of 
the  solution  and  the  solubility  of  the  substances  present  of  it, 
and  let  us  restrict  the  influence  of  temperature,  pressure,  and 
time  by  choosing  a  definite  point,  25°,  for  the  first,  atmos- 
pheric pressure  for  the  second,  and  crystallization  in  the 
manner  common  in  laboratories  for  the  third.  In  this  way 
we  approach  most  closely  the  conditions  of  Usiglio's  experi- 
ments, while  considering  the  problem  involved  in  the  gradual 
removal  of  the  solvent  as  a  general  one.  The  concentration 
of  sea- water  will  thus  arise  as  a  special  case,  when  in  the 
course  of  this  more  general  study  the  constituents  of  sea- 
water  receive  special  consideration. 

Among  the  constituents,  of  course,  the  amount  of  sodium 
chloride  occupies  the  place  of  chief  importance.  After  it 
come  the  chlorides  and  sulphates  of  magnesium  and  potas- 
sium. Thirdly,  there  are  the  calcium  salts,  and  with  these,  for 
our  present  purpose,  the  list  closes.  Now,  in  order  to  give 
a  clear  view  of  the  composition  of  sea-water,  let  us  express 
the  proportion  of  the  constituents,  which,  strange  to  say,  if 
we  exclude  the  calcium  salts,  is  the  same  all  over  the  earth, 
in  molecules: 

lOONaCl-f-  2.2KC1  +7.8MgCl2  +3.8MgSO4  . 


102  PHYSICAL  CHEMISTRY 

Let  us  now  develop  the  laws  pertaining  to  the  crystalliza- 
tion, step  by  step,  taking  the  dissolved  substances  into  account 
one  by  one. 

If  a  single  salt  is  present  the  situation  is  very  simple. 
As  evaporation  takes  place  the  saturation  point  is  finally 

reached  and  the  salt  in  question 
separates  out  until  the  whole  has 
dried  up.  So  soon,  however,  as 
two  salts  are  present,  the  ques- 
tion arises,  Which  will  crystallize 
first,  and  when  will  the  second 
appear?  Let  us  answer  this 
question,  taking  as  the  two  salts 
potassium  chloride  and  sodium 
FIG.  7  chloride  at  25°.  We  have  only 

to  remember  that  if,  for  example,  the  solution  contains  so 
much  potassium  chloride  that  this  salt  is  the  first  to  separate 
in  the  solid  form,  further  concentration  must  gradually 
increase  the  content  of  sodium  chloride  until  this  substance 
also  begins  to  appear.  From  this  moment  onward  the  solu- 
tion retains  its  composition  unchanged.  It  simply  dimin- 
ishes in  volume  and  deposits  both  salts  until  the  solvent  is 
all  gone.  Obviously  the  same  ultimate  solution  must  be 
obtained  if  we  start  from  the  opposite  side  with  a  sufficient 
excess  of  chloride  of  sodium.  The  whole  situation  is  thus 
clear  when  we  know  the  composition  of  the  final  solution 
which  is  saturated  with  both  salts.  Analysis  of  a  solution 
which  has  been  agitated  for  a  sufficient  length  of  time  with 
an  excess  of  both  salts  at  25°  gives  the  following  result: 


GEOLOGY  103 


[100H2O  +  89NaCl  +  39KC1]  (C,  Fig.  7). 

Thus,  solutions  which  contain  a  greater  ratio  of  sodium 
chloride  to  potassium  chloride  than  89  X  58.5  :  39  X  74.5  will 
first  deposit  sodium  chloride.  In  the  opposite  case  potassium 
chloride  will  first  appear. 

Here,  then,  the  relations  are  still  of  a  simple  character. 
In  order  that  they  may  retain  their  comprehensibility  when 
applied  to  more  complicated  cases,  let  us  represent  them 
graphically  as  in  Fig.  7.  To  complete  the  figure,  we  require 
the  solubility  of  sodium  chloride,  which  is  expressed  by  the 

formulae 

[1000H2OH-lllNaCl]  (A,  Fig.  7), 

and  that  of  potassium  chloride,  which  is 

[1000H2O  +  88KC1]  (B,  Fig.  7). 

Now,  with  O  as  origin,  let  us  lay  off  the  amount  of  sodium 
chloride  in  the  vertical  direction  and  that  of  potassium 
chloride  horizontally  to  the  right.  When  this  is  done  the 
data  given  above  lead  to  three  points,  which  we  have  desig- 
nated in  order  C,  A,  B,  and  if  we  now  connect  A  and  B  with 
C  the  line  AC  represents  saturation  with  sodium  chloride, 
while  the  proportion  of  potassium  chloride  increases.  Simi- 
larly, the  line  BC  stands  for  saturation  with  potassium 
chloride,  while  the  content  of  sodium  chloride  increases. 

It  is  now  easy  to  see  what  must  take  place  when  any 
solution  is  concentrated.  Let  it  be  an  unsaturated  one, 
corresponding  in  composition  to  a  point  c  inside  the  area 
OACB,  its  situation  being  given  by  the  proportions  of  the 
respective  chlorides.  When  evaporation  begins,  the  relative 


104  PHYSICAL  CHEMISTRY 

proportions  of  the  chlorides  do  not  alter,  but  their  quantity, 
calculated  on  the  basis  of  the  number  of  molecules  in  every 
1000H2O,  must  increase.  This  change  corresponds  to  a 
motion  away  from  O  along  a  straight  line  connecting  O  with 
c,  that  is  to  say,  a  motion  along  cd.  When  BC  is  encoun- 
tered at  d,  this  means  that  separation  of  potassium  chloride 
begins,  and  here  a  change  in  the  direction  of  the  motion 
occurs  which  reflects  an  ensuing  phenomenon.  The  direc- 
tion taken  is  now  towards  C,  or,  in  other  words,  is  away  from 
B  in  the  direction  of  the  arrow.  When  C  is  reached,  sim- 
ultaneous separation  of  both  salts  begins,  and  this  stage 
reaches  its  conclusion  when  the  solution  has  dried  up.  This 
must  ultimately  occur  to  every  solution  after  this  point  has 
been  reached,  and  we  therefore  name  C  the  final  point  of 
crystallization. 

We  may  now  read  in  this  graphic  representation  the  law 
upon  which  ultimately,  even  in  the  most  complicated  cases, 
the  progress  of  crystallization  is  founded.  In  words,  it 
amounts  to  this,  that  in  depositing  its  contents  the  solution 
gradually  varies  its  composition  away  from  that  of  a  solution 
which  is  saturated  with  the  substance  being  deposited  at  the 
moment  and  contains  nothing  but  this  substance.  The  prin- 
ciple becomes  quite  clear  if  we  reverse  the  process  which  takes 
place  during  crystallization  from  an  evaporating  solution, 
i.  e.,  if  we  add  continually  water  and  the  salt  which  is  being 
deposited.  Under  these  circumstances  obviously  the  solution 
tends  to  become  more  and  more  a  saturated  solution  of 
this  salt  alone,  since  the  other  constituents,  whatever  they 
may  be,  must  gradually  become  relatively  negligible  in 
quantity. 


GEOLOGY  105 


In  the  graphic  representation  given  in  Fig.  7  we  may 
perceive  four  applications  of  this  law.  If  potassium  chlo- 
ride separates  on  BC  we  move  in  the  direction  away  from  B, 
where  saturation  with  potassium  chloride  is  represented;  if 
sodium  chloride  appears  upon  AB  we  move  away  from  A, 
where  saturation  with  sodium  chloride  exists.  If  both  salts 
are  deposited  at  C,  we  remain  at  rest  at  C,  since  we  can 
move  neither  towards  A  nor  towards  B,  and  everything  else 
is  excluded.  If  nothing  separates  at  c,  we  proceed  in  the 
direction  away  from  O,  where  the  solution  contains  nothing 
whatever.  All  this,  which  in  the  present  case  is  obvious, 
will  later  furnish  us  with  valuable  guidance.  Let  us  proceed 
then  to  the  consideration  of  a  more  complicated  case. 

Keeping  the  salts  found  in  sea-water  in  view  and  .look- 
ing at  the  composition  of  sea-water, 

[lOONaCl  +  2 .  2KC1  -f  7 . 8MgCl2  +  3 .  8MgSO4]  , 

we  could  now  add  to  the  combination  sodium  chloride  and 
potassium  chloride,  a  third  salt,  e.  g.,  magnesium  chloride. 
We  shall  reach  the  goal  more  quickly,  however,  if  we  first 
consider  the  salts  potassium  chloride,  magnesium  chloride, 
and  magnesium  sulphate,  and  only  at  the  very  end  take  into 
consideration  the  chloride  of  sodium,  which  is  always  pres- 
ent in  excess. 

Proceeding  systematically  we  have  first  the  combination 
potassium  chloride  and  magnesium  chloride,  that  is  to  say, 
a  combination  with  a  common  acid,  then  that  of  magnesium 
chloride  and  magnesium  sulphate  with  a  common  base. 
Further,  however,  if  the  problem  is  stated  in  a  general  form, 
potassium  sulphate,  which  has  not  been  mentioned,  must  be 


106 


PHYSICAL  CHEMISTRY 


taken  into  account,  since  it  may  arise  out  of  potassium 
chLpride  and  magnesium  sulphate.  The  third  combination 
is  thus  magnesium  sulphate  and  potassium  sulphate  with  a 
common  acid,  and  the  last  will  be  potassium  sulphate  and 
potassium  chloride  with  a  common  base. 

Let  us  now  collect  into  one  table  the  data  in  regard  to 
solubility  which  are  required  as  the  basis  of  graphic 
representation  for  this  cycle  of  substances.  Three  of  them 
have  just  been  given.  For  the  present  purpose,  however, 
we  now  represent  all  the  salts  in  equivalent  amounts,  so  that 
potassium  chloride  is  in  double  molecules. 


OATUKATION  WITH 

K,C12 

MgCl2 

MgS04 

K2SO< 

A   Potassium  chloride  

44 

E.  Potassium  chloride  and  carnallite  

&A 
1 

72^ 
105 

.... 

.... 

B   Magnesium  chloride  

108 

G  Magnesium  chloride  and  MgSO4  .  6H2O    . 

104 

14 

H  MgSO     7H2O  and  MgSO4   6H3O 

73 

15 

C  MgSO4.7H2O  

55 

J  MgSO4   7H2O  and  schonite.  .  .            

58  U 

5^ 

K  Potassium  sulphate  and  schonite 

22 

16 

D  Potassium  sulphate.                 

12 

Li   Potassium  sulphate  and  potassium  chloride 

42 

VA 

IN  MOLS.  PER  1000  MOLS.  H* 


The  presentation  of  the  whole  of  this  material  graphically 
makes  the  understanding  of  it  much  easier.  The  rectangular 
axes  in  the  plane  of  the  paper  can  be  retained  and  from 
their  point  of  intersection  at  O  (Fig.  8)  the  four  single 
salts,  potassium  chloride,  magnesium  chloride,  magnesium 
sulphate,  and  potassium  sulphate,  can  be  laid  off  in  the 


GEOLOGY 


107 


FIG. 


directions,  A,  B,  C,  and  D,  respectively.  The  four  combina- 
tions which  they  form,  two  by  two,  fall  then  within  the 
quadrants  lying  between  the  axes.  We  obtain  in  this  way  a 
fashion  of  representing  the  facts  something  like  Fig.  7 


108  PHYSICAL  CHEMISTRY 

repeated  four  times.  In  this  case,  however,  in  three  of  the 
quadrants  a  complication  arises  from  the  existence  of  an  inter- 
mediate compound.  Between  A,  saturation  with  potassium 
chloride,  and  D,  saturation  with  potassium  sulphate,  there  is 
only  the  point  L,  where  the  solution  is  saturated  with  both. 
Between  A  and  B,  however,  carnallite  (KC1 .  MgCl2  .  6H2O) 
appears,  and  thus  two  determinations  are  necessary,  which 
have  been  added  at  E  and  P  and  stand  for  saturation  with 
carnallite  and  potassium  chloride  in  the  one  case,  and  the 
same  compound  with  magnesium  chloride  in  the  other.  In 
the  same  fashion  between  B  and  C  magnesium  sulphate  with 
six  molecules  of  water  crystallization  appears  in  GrH  and  be- 
tween C  and  D  the  mineral  schonite  (K2Mg(SO4)2-f6H2O) 
along  JK.  The  progress  of  crystallization,  using  the 
same  principle  as  before,  is  just  as  easy  to  follow,  and  is 
indicated  by  the  arrows  which  in  each  quadrant  are  directed 
towards  a  so-called  final  point  of  crystallization.  In  this 
diagram  these  points  are  F,  G,  J,  and  L. 

So  far,  however,  we  have  only  considered  a  part  of  the 
possibilities,  for  solutions  are  entirely  lacking  which  contain 
everything,  that  is  to  say,  chlorine  and  sulphuric  acid, 
potassium  and  magnesium.  The  experimental  treatment  of 
this  question  may  best  be  shown  by  means  of  an  example. 
Let  us  start  from  L  (Fig.  8),  where  the  solution  at  25°  is 
saturated  with  potassium  chloride  and  potassium  sulphate 
simultaneously.  Taking  care  that  both  potassium  salts  are 
present  in  excess  and  in  contact  with  the  solution,  we  add 
magnesium  in  the  form  of  chloride  or  sulphate.  The  solu- 
tion then  takes  up  magnesium,  but  remains  still  saturated 


GEOLOGY  109 


with  potassium  sulphate  and  potassium,  chloride.  Finally 
its  capacity  for  taking  up  magnesium  becomes  exhausted, 
and  a  solid  magnesium  salt  is  deposited.  This  in  the  case 
before  us  is  schonite  (K2Mg(SO4)2  .  6H2O).  After  this,  fur- 
ther addition  of  the  magnesium  salt  will  not  lead  to  any  being 
dissolved  ;  the  consequence  will  simply  be  an  increase  in  the 
amount  of  schonite.  The  solution  will  retain  its  constant 
composition,  since  it  is  and  remains  saturated  with  potassium 
sulphate  and  potassium  chloride.  We  determine  the  com- 
position of  this  solution  by  analysis,  using  a  mixture  which 
at  25°  after  prolonged  agitation  is  seen  to  be  in  contact  with 
all  the  three  salts  and  is  found  to  have  attained  a  constant 
composition.  The  result  is  represented  by  the  following 
formula : 

[1000H20  -f  25K2C12  +  HMgS04  +  21MgCl2]  . 

Our  task  is  thus  finally  limited  to  finding  the  solutions 
saturated  with  three  salts  and  analyzing  those  solutions. 
Many  such  are  a  priori  possible,  if  we  consider  the  seven 
different  compounds  which  have  to  be  taken  into  account. 
The  possible  number  would  be: 

7x6x5 


1x2x3 


-=35  . 


As  a  matter  of  fact,  however,  only  a  few  of  these  possibili- 
ties are  realized,  and  when  a  solution  obtained  in  the  above 
manner  is  systematically  evaporated  at  25°,  and  the  salt 
deposits  are  continually  removed,  the  possibilities  which  are 
actually  realized  are  found  to  be  limited  to  four,  in  addition 
to  the  one  described. 


110 


PHYSICAL  CHEMISTRY 


After  potassium  chloride  and  schonite  have  come  out, 
magnesium  sulphate  with  seven  molecules  of  water  of  crys- 
tallization appears  as  an  additional  salt.  The  deposit  having 
been  removed,  this  hydrate  of  magnesium  sulphate  and 
potassium  chloride  are  now  deposited  until  finally  magne- 
sium sulphate  with  six  molecules  of  water  of  crystallization 
is  added  to  these  two  salts  as  a  new  constituent.  From  this 
point  onward  the  hexahydrate  of  magnesium  sulphate  with 
potassium  chloride  crystallizes  until  carnallite  makes  its 
appearance.  After  this  the  hexahydrate  of  magnesium  sul- 
phate with  carnallite  constitute  the  deposit  until  magnesium 
chloride  appears,  and  now  the  solution  dries  up  completely  to 
a  mixture  of  the  three  last-named  substances. 

Collecting  once  more  the  quantitative  measurements  con- 
nected with  these  deposits,  we  have  the  following  table: 


IN  MOLS.  PEE  1,000  MOLS.  H2O 


SATURATION  WITH 

K2Cla 

MgCla 

MgS04 

M.  Potassium   chloride,    potassium    sulphate, 
schonite  

25 

21 

11 

N.  Potassium  chloride,  MgSO4  .7H,O,  schonite 
P.  Potassium  chloride,  MgSO4.  7H2O,  MgSO4 
6H  O 

9 

8 

55 
G2 

16 
15 

Q.  Potassium     chloride,    carnallite,     MgSO4 
6H8O                                        

4M 

70 

13^ 

R.  Magnesium    chloride,    carnallite,    MgSO4 
6H8O  

2 

99 

12 

The  next  thing  is  to  represent  these  numbers  graphically, 
and  when  this  has  been  done  we  are  presented  with  a 
complete  view  of  the  whole  process  of  crystallization. 


GEOLOGY  111 


To  do  this  a  third  dimension  is  obviously  required.  We 
add  a  third  axis  passing  through  O,  vertical  to  the  former 
system  of  axes  (Fig.  8),  and  along  this  we  lay  off  the  number 
of  molecules.  In  practice  this  may  be  done  conveniently  by 
means  of  a  model  consisting  of  a  piece  of  wood  in  which 
vertical  needles  are  set  at  the  proper  places,  with  their 
lengths  adjusted  to  the  number  of  molecules.  A  horizontal 
projection  on  this  model  is  shown  in  Fig.  9,  whose  border 
obviously  coincides  with  the  outline  of  Fig.  8,  and  whose 
points  M,  N,  P,  Q,  and  R  represent  the  above  data.1  This 
having  been  done,  each  pair  of  points  representing  satura- 
tion with  the  same  two  salts — for  example,  M  and  L,  where 
in  both  cases  saturation  with  the  sulphate  and  chloride  of 
potassium  exists— is  connected  by  a  line. 

These  lines  divide  the  figure  into  areas,  each  of  which 
corresponds  to  saturation  with  a  definite  salt,  as  follows: 

EQPNMLA  -      Potassium  chloride 

EQRF    -  Carnallite 

FRGB  -     Magnesium  chloride 

RGHPQ  MgS04.6H20 

PHCJN  -     MgSO4.7H2O 

JKMN  SchOnite 

KMLD  -    Potassium  sulphate 

The  progress  of  crystallization  is  given  in  each  area  by 
lines  which  proceed  away  from  the  points  which  represent 
saturation  with  the  body  itself,  as  a  single  constituent. 
Thus,  in  the  potassium  chloride  area,  these  lines  proceed 
from  A  in  all  directions. 

i  It  may  be  remarked  that  this  method  of  presenting  the  facts  is  not  influenced 
by  the  condition  in  which  one  supposes  the  salts  to  be  present  in  the  solution ;  that 
is  to  say,  whether  they  are  K2C1,  and  MgSO4  or  MgCl,  and  K,SO4 . 


112 


PHYSICAL  CHEMISTRY 


D 


FIG.  9 


Let  us  apply  this  now  to  a  particular  case,  taking,  for 
example,  a  solution  containing  a  gram-molecule  of  magne- 
sium chloride  and  a  gram-molecule  of  potassium  sulphate. 
The  preliminary  evaporation  without  any  deposit  appearing 


GEOLOGY  113 


corresponds  to  motion  from  the  origin  in  the  vertical  direc- 
tion until  the  area  lying  immediately  above  it  —  that  is  to 
say,  the  potassium  sulphate  area — is  encountered.  Potas- 
sium sulphate  should  separate  out,  and  this,  as  a  matter  of 
fact,  is  just  what  occurs.  We  next  expect  a  movement 
away  from  D  until  the  limit  KM  is  reached,  where 
schonite  should  appear,  and  this  expectation  is  also  fulfilled 
in  practice.  If  the  salts  as  they  come  out  are  always 
removed,  the  deposition  of  schonite  corresponding  to  a 
movement  across  the  schonite  area  in  the  direction  of  the 
lines  drawn  upon  it  takes  place  until  MN  is  reached,  indicat- 
ing the  beginning  of  potassium  chloride  crystallization. 
This  salt  does  actually  appear  next.  Here  the  course  of  the 
paths  of  crystallization  from  both  sides  shows  that  with  fur- 
ther concentration  we  remain1  on  the  line  MN  until  at  N 
magnesium  sulphate  begins  to  be  deposited.  The  rest  of 
the  changes  may  be  read  from  the  diagram  in  the  same 
manner.  Not  only  can  we  thus  follow  the  progress  of  the 
crystallization,  qualitatively,  however.  We  can  calculate 
the  quantity  of  each  substance  which  will  be  separated  when 
a  given  point  corresponding  to  a  known  composition  is 
reached.  The  results  agree  exactly  with  experiments  which 
have  been  made  in  a  variety  of  ways.  Thus  Fig.  9  contains 
the  basis  for  understanding  and  even  predicting  the  whole 
process  of  crystallization. 

When  a  beginning  has  been  made  in  applying  the  prin- 
ciples according  to  which  crystallization  proceeds,  the  addi- 

i  For  this  reason  boundaries  like  MN  are  named  bases  of  crystallization.  There 
are  four  of  these  proceeding  from  the  final  points  of  crystallization,  L,  J,  G,  and  F. 
All  meet  together  at  the  common  final  point  B. 


114  PHYSICAL  CHEMISTRY 

tional  compounds  occurring  in  the  natural  deposits  can 
easily  be  introduced  into  the  scheme.  These  are  sodium 
chloride  and  the  salts  of  calcium. 

We  shall  not  attempt  to  carry  out  this  extension  in 
detail.  It  may  simply  be  mentioned  that  a  scheme  corre- 
sponding to  Fig.  9  can  be,  and  has  been,  laid  out  for  the  case 
in  which  all  the  solutions  are  saturated  with  sodium  chloride 
at  25°,  a  state  which  corresponds  with  natural  conditions. 
So  far  as  the  salts  of  calcium  are  concerned,  their  solubility 
is  so  small  that  they  do  not  seriously  alter  the  composition 
of  the  solutions  themselves.  It  is  only  necessary  to  de- 
termine from  which  of  the  solutions  calcium  in  the  form 
of  gypsum  (CaSO4.2H8O),  anhydrite  (CaSO4),  syngenite 
(CaSO4.K8SO4.H8O),  or  some  other  form,  will  be  de- 
posited. 


LECTURE  IX 

PHYSICAL  CHEMISTRY  AND  GEOLOGY 

The  Influence  of  Time  and  of  Variations  in  Temperature  and  Pressure 
on  Deposition — The  Time  Factor  and  Delayed  Crystallization  — 
Several  Compounds,  Found  in  Nature,  Do  Not  Appear  at  All  in 
Laboratory  Experiments  on  Deposition,  but  Can  Be  Included  in 
the  Scheme  by  the  New  Method  of  Agitation  with  Solutions  — 
The  Behavior  at  Temperatures  above  25° — New  Minerals  Formed 
above  25°  and  Absent  at  25° — New  Combinations  of  Minerals 
Possible  above  25° — Disappearance  above  25°  of  Minerals  Formed 
at  that  Temperature — The  Influence  of  Possible  Changes  in 
Pressure  Too  Slight  to  Affect  the  Results. 

THAT  to  which  in  this  second  lecture  on  geology  I  should 
like  chiefly  to  devote  my  attention  is  the  consideration  of  the 
parts  which  time,  temperature,  and  pressure  play  in  modify- 
ing the  nature  or  amount  of  the  deposits.  Their  impor- 
tance diminishes  in  the  order  stated. 

Time  is  the  most  important  factor,  and  yet  its  influence 
is  the  most  difficult  of  the  three  to  determine  by  laboratory 
experiments.  In  direct  experiments  on  the  crystallization 
of  sea-water,  such  as  were  made  by  Usiglio,  obviously  time 
received  less  consideration  than  anything  else,  and  a  better 
approach  to  a  knowledge  of  the  geological  processes  is 
hardly  possible  by  his  method,  in  consequence  of  the  speed 
of  the  experiments.  The  method  of  treating  the  subject 
described  here  is  more  favorable  in  this  respect.  At  first  it 
is  true  the  results  accord  essentially  with  those  of  Usiglio. 
In  the  course  of  further  investigation,  however,  one  com- 

115 


116  PHYSICAL  CHEMISTRY 

pound  after  another  is  obtained  which,  on  account  of 
retardation  of  quite  unexpected  extent,  is  entirely  missed 
when  the  ordinary  method  of  crystallization  is  employed. 
Such  retardations  are  known  to  you  in  the  case  of  so-called 
supersaturated  solutions,  such  as  that  of  Glauber's  salt. 
Supersaturations  of  this  kind,  however,  are  easy  to  avoid  by 
introduction  of  the  substance,  here  Glauber's  salt,  in  respect 
to  which  supersaturation  exists.  In  imitation  of  this  we 
have  always  prepared  our  saturated  solutions  by  long  agita- 
tion with  the  salts  in  respect  to  which  saturation  is 
required.  After  this  has  been  done,  a  filtered  sample  is 
brought  in  contact  with  well-developed  crystals  of  the  same 
salts,  in  order  that  the  question  of  the  existence  of  satura- 
tion may  be  definitely  settled.  This  procedure  had  seemed 
to  make  success  only  a  question  of  hours,  or  at  most  of 
days,  until  we  unexpectedly  found  that  some  compounds 
whose  formation  in  the  solutions  under  investigation  was  pos- 
sible at  25°,  nevertheless  totally  failed  to  put  in  an  appear- 
ance. These,  not  to  mention  the  salts  of  calcium,  were 
leonite,K3Mg(SOJ2  .4H2O;  kainite,  MgSO4  .  KC1.3H2O; 
and  kieserite,  MgSO4.H2O.  Even  exceedingly  slow  crys- 
tallization with  the  addition  of  the  compounds  themselves 
did  not  remove  the  condition  of  supersaturation  in  the  case 
of  these  bodies. 

Precisely  in  this  region  the  new  method  of  treatment 
shows  its  superiority,  since  it  is  not  dependent  upon  direct 
crystallizations.  It  relies  on  the  determination  of  solubility 
data,  and  relatively  few  of  these,  to  give  a  complete  view 
of  the  whole  plan  of  crystallization,  both  qualitatively  and 


GEOLOGY 


117 


quantitatively.  Now,  data  of  this  kind,  in  the  case  of  the 
bodies  just  mentioned,  may  be  obtained  in  spite  of  the 
tendency  to  retardation,  although  agitation  may  sometimes 
have  to  be  continued  for  weeks. 

Let  us  now  present  the  data  obtained  from  such  experi- 
ments : 


SATURATION  WITH  SODIUM  CHLORIDE 


AND 

Na,Cl, 

K,C1, 

MgCl, 

MgS04 

Na7S04 

o 

551^ 

A    MgCla  6HaO 

2U 

103 

B    KC1 

44^ 

19i/ 

C.    Na2SO4          .     .              

51 

12^ 

D    MgCla  6H2O,  carnallite 

1 

U 

103^ 

E.    KC1,  carnallite   

2 

&A 

70^ 

F.   KC1,  glaserite 

44 

20 

4^ 

G.    Na2SO4,  glaserite  

44^ 

IOK 

14^ 

H.  Na8SO4,  astrakanite  

46 

iw 

3 

I      MgSO4  .7HaO,  astrakanite  . 

26 

7 

34 

J.    MgSO4.7H2O,MgSO4.6H2O.... 
K.   MgSO4  .  6H2O,  kieserite  

4 

2^ 

.... 

67^ 
79 

12 
9^ 

.... 

L     Kieserite  MgCl2.6H2O 

1 

102 

5 

M.  KOI,  glaserite,  schdnite  

23 

14 

21  y» 

14 

N.    KC1,  schonite,  leonite  

14 

11 

37 

14^ 

P.    KC1,  leonite,  kainite  . 

9 

9^ 

47 

14^ 

Q.    KC1,  kainite,  carnallite  

2^ 

6 

68 

5 

R.    Carnallite,  kainite,  kieserite  
S.    Na2SO4,  glaserite,  astrakanite  .  .  . 
T.    Glaserite,  astrakanite,  schonite  .  . 
U.   Leonite,  astrakanite,  schonite  
V.    Leonite,  astrakanite, 
MgSO4  .  7H2O  

yz 

42 

27^ 
22 

1(W 

1 

8 

IOK 

10K 

7^ 

85^ 

16K 
23 

42 

8 
16 

18& 
19 

19 

6 

W.  Leonite,  kainite,  MgSO4  .  7H,O  .  . 
X.  MgSO4.6H2O,  kainite, 
MgSO4.7H8O  

9 

3*4 

ty* 

4 

45 
65^ 

19^ 
13 



Y.    MgSO4  ,6H2O,  kainite,  kieserite  . 
Z.    Carnallite,  MgCl,.  6H2O,  kieserite 

VA 

0 

2 

H 

77 
100 

10 
5 

.... 

MOLS.  WITH  1000  MOLS.  H,O 


118 


PHYSICAL  CHEMISTRY 


Those  data  may  be  represented  by  a  model,  in  the  way 
previously  described.  A  projection  of  this  model  is  shown 
in  Fig.  10.  The  basal  plane  is  in  so  far  different  that  the 
sodium  chloride  is  not  represented  in  the  model,  while  the 
sodium  sulphate  is  not  taken  into  account  in  the  number 
of  molecules,  in  consequence  of  the  relation 

Na2SO4  =  Na2Cl2  +  MgSO4  -  MgCl2 

The  latter  is  measured  off  upon  an  axis  OC,  which  bisects 
the  angle  DOB.  The  areas  correspond  to  the  following 
substances : 


Area 

Formula 

Mineralogical  Name 

1.  ALZD   

MgCl2.6HoO 

Bischofite 

2   BFMNPQE 

KC1 

Sylvite 

3  CGSH 

Na2SO4 

Thenardite 

4.  DZRQE  

KMgCl3.6H2O 

Carnallite 

5.  FMTSG  
6.  SHIVUT  
7.  JXWVI  

K3Na(S04)2 
Na2Mg(S04)2  .  4H30 
MgSO4.7H2O 

Glaserite 
Astrakanite 
Reichardtite 

8  JXYK  

MgSO4.6H2O 

(Not  found) 

9.  KYRZL  
10  TUNM 

MgSO4.H3O 
K9Me(S(X),     6H9O 

Kieserite 
Schonite 

11   NUVWP  

KoMg(SO,)o,    4HaO 

Leonite 

12  PWXYRQ 

MgSO4.KC1.3H^O 

Kainite 

and  the  progress  of  crystallization  may  be  developed  on  the 
same  principle  as  before. 

The  next  thing  to  be  considered  is  the  influence  of  tem- 
perature. Solubility  is,  as  we  all  know,  very  generally  influ- 
enced by  change  of  temperature,  and  such  a  change  will 
therefore  alter  a  diagram  constructed  for  25°.  For  our  pur- 
pose it  is  important  to  determine  what  geological  information 


GEOLOGY 


119 


120  PHYSICAL  CHEMISTRY 

may  be  obtained  in  this  direction.  The  most  significant 
thing  is  the  appearance  of  additional  minerals  which  cannot 
be  formed  as  low  as  25°.  Then  follows  the  appearance  of 
additional  combinations  of  minerals.  Finally  the  disappear- 
ance of  some  minerals  is  to  be  noted. 

Among  the  appearances  of  minerals  at  temperatures 
above  25°  two  may  be  mentioned  by  way  of  illustration. 
Among  the  chlorides  and  sulphates  of  potassium,  magnesium, 
and  sodium,  two  known  materials  are  absent  at  25°,  namely 
langbeinite,  K2Mg2(SO4)3,  and  loeweite,  Na2Mg(SO4)2  . 
2H2O.  The  failure  of  these  substances  to  appear  is  not  a 
consequence  of  retardation,  for  in  the  solutions  in  which  at 
25°  they  would  first  be  formed,  they  are  actually  decomposed 
by  interaction  with  water.  Thus  langbeinite  becomes  a  mix- 
ture of  magnesium  sulphate  and  leonite  according  to  the 
equation : 

K2Mg2(SO4)3  +  11H2O  =  MgSO4  .  7H2O  + 

K2Mg(S04)2  .  4H20 
and  loeweite  gives  astrakanite: 

Na2Mg(SOT)2  .  2H2O  +  2H2O  =  Na2Mg(SO4)2  .  4H2O  . 

This  fact  furnishes  us  with  a  hint  in  the  determination  of  the 
temperature  at  which  these  bodies  would  be  formed.  The 
products  of  their  hydration  have  only  to  be  heated  in  con- 
tact with  that  solution  which  is  saturated  with  them,  and 
possesses  the  greatest  water- withdrawing  power.  In  the  case 
of  langbeinite  this  is  the  solution  W  (Fig.  10),  where  the 
necessary  saturation  with  magnesium  sulphate  and  leonite 
exists,  and  where,  besides,  kainite,  with  which  the  solution 


GEOLOGY  121 


is  simultaneously  saturated,  contributes  to  the  water-remov- 
ing power.  In  contact  with  this,  langbeinite  is  formed  from 
its  products  of  hydration  above  37°,  while  below  this  tem- 
perature the  change  is  reversed.  The  occurrence  of  lang- 
beinite in  the  natural  salt  deposits  thus  indicates  the  existence 
of  a  temperature  above  37°.  A  similar  temperature  limit  of 
43°  is  found  for  loeweite. 

Let  us  now  turn  to  the  second  influence  of  temperature, 
that,  namely,  on  the  simultaneous  occurrence  of  minerals. 
This  is  shown  in  Fig.  10  for  the  temperature  25°.  We  shall 
present  the  same  figure  in  a  simplified  form,  preserving  all 
the  lines  of  contact,  but  changing  shapes  of  the  areas  to 
rectangles.  We  then  see  that  glaserite,  for  example,  can 
occur  along  with  astrakanite,  but  not  along  with  bischofite. 
This  figure  (Fig.  11)  contains  material  for  a  great  number  of 
geological  inferences. 

When  I  was  exhibiting  Fig.  11  in  a  lecture  on  this  subject 
in  Strassfurt,  Dr.  Schwab  directed  my  attention  to  "hartsalz," 
a  mixture  of  kieserite  and  potassium  chloride,  which  is 
excluded  at  25°,  since  the  two  areas  are  separated  by  kainite. 
This  problem  was  taken  up  by  Meyerhoffer,  who  found  that 
"hartsalz"  is  a  product  peculiar  to  a  much  higher  tempera- 
ture, somewhere  in  the  neighborhood  of  70°.  This  tempera- 
ture is  probably  the  highest  of  which  we  have  any  indication 
in  connection  with  this  subject. 

The  third  point,  the  disappearance  of  some  minerals,  might 
also  be  employed  as  a  geological  thermometer.  Thus,  the 
existence  of  reichardtite,  MgSO4  .  7H2O,  is  determined  by 
an  upper  limit  of  47°,  that  of  schonite  by  the  temperature 


122 


PHYSICAL  CHEMISTRY 


Finally  the  pressure  must  be  considered.  It  has  often 
been  hinted  at  as  a  possible  agency  in  the  formation  of 
minerals,  which,  like  anhydrite,  fail  to  appear  in  laboratory 


A 


L 

K 

J 

I 

H 
C 

Bischofite 
MgCl2  .  6H2O 

I) 
E 

B 

z 

Kieserite                                            Carnallite 
MgSO4  .  H2O                                  KMgCl3  .  6H,O 

Y 
MgS04.6H20 

R 

Kainite 
MgSO4.KC1.3HsO 

Q 

p 

Sylvite 
KC1 

N 

M 

X 

Reichardtite 
MgSO4  .  7H2O 

Leonite 
K2Mg(S04)2.4H20 

V 

U 
Astrakanite 
Na2MgiSO4)2.4H2O 
T 
S 

Schonite 
K3Mg(S04)2.6H80 

Glaserite 
K3Na(S04)2 

Thenardite 
Na2S04 

G 


F 


FIG.  11 


experiments,  when  the  cause  of  this  was  simply  retardation. 
On  reflection  we  find  that  the  influence  of  pressure  in  the 
formation  of  natural  salts  must  be  relatively  small.  In  the 
case  of  the  Strassfurt  deposits,  for  instance,  we  cannot  count 
upon  a  greater  depth  of  sea-water  than  1500  meters. 


GEOLOGY  123 


Assuming  the  specific  weight,  when  the  deposition  of  salts 
begins,  to  be  1.2,  this  would  indicate  a  pressure  of 

1500  X  1.2 


-  1°0  atmospheres 

Now,  the  chief  effect  of  the  pressure  is  that  temperatures 
of  formation,  such  as  the  37°  in  the  case  of  langbeinite,  are 
displaced.  They  are  raised  when,  as  is  commonly  the  case 
with  actions  involving  the  separation  of  water,  a  simultaneous 
expansion  takes  place. 

The  extent  of  these  displacements  is,  however,  of  the 
same  order  as  that  which  the  melting-points  show  under  the 
influence  of  the  same  agency.  It  may  be  determined  theo- 
retically. We  have  measured  it  experimentally  also  in  con- 
nection with  the  formation  of  the  mineral  tachhydrite, 
Ca(MgCl3)2  .  12H2O,  with  the  anticipated  result.  It  was 
found  that  a  single  atmosphere  of  pressure  only  affected  the 
temperature,  here  22°,  by  a  few  thousandths  of  a  degree.  The 
actual  measurement  was  0.017°,  which  for  180  atmospheres 
would  correspond  to  3°. 

Since  in  the  case  of  the  formation  of  salt  deposits, 
according  to  the  latest  direct  observations  with  the  salt 
mother-liquors  of  Siebenburgen  by  Kaleczinsky,1  changes  in 
temperature  of  50°  have  to  be  reckoned  with,  the  considera- 
tion of  pressure  is  very  much  less  important  in  the  study  of 
this  problem  than  is  that  of  temperature. 

1  Uber  die  ungarischen  warmen  und  heissen  Kochsalzseen,  Budapest,  1901. 


INDEX 


ACETIC  ACID,  87. 

ALCOHOL,  87. 

AMYGDALIN,  84, 92. 

ANHYDRITE,  99, 100, 

ARRHENIUS,  24,  39. 

ASTBAKANITE,  118. 

AVOGADKO'S  LAW,  17;  applied  to  solu- 
tions, 19,  73. 

BAKER,  91. 

BAKHUIS-ROOZEBOOM,  25,  67. 

BECKMANN,  81. 

BENZALDEHYDE,  84, 92. 

BERTHELOT,  17,  31,  33,  87. 

BISCHOFITE,  118. 

CALCIUM  CARBONATE,  100. 

CARNALLITE,  99, 100;  graphic  represent- 
ation of  its  region  of  stability,  29 ;  illus- 
trating the  new  and  comprehensive 
method  of  studying  a  problem,  25; 
method  of  manufacturing  potassium 
chloride  from,  48;  three  methods  of 
splitting  up,  50;  transition  point  at 
—21%  27, 34 ;  transition  point  at  168",  28. 

CARNOT-CLAUSIUS  PRINCIPLE,  20. 

CAST  IRON,  white  and  gray,  67. 

CATALYTIC  ACTION,  85. 

CEMENTITE,  61. 

COHEN,  53,  75. 

CONSERVATION  OP  ENERGY,  20. 

CRYSTALLIZATION:  final  point  of,  104; 
graphic  representation  of,  102, 107, 112, 
119, 122. 

DANIELL  CELL,  36. 

DEPOSITION:  influence  of  pressure  on, 
122;  influence  of  temperature  on,  118; 
influence  of  time  on,  115. 

DB  VRIES,  74. 

DILATOMETER;  use  of,  in  determining 
transition  point  of  tin,  55. 

BONDERS,  77. 

DUHEM,  6 


ELECTRICAL  METHOD:  of  determining 
transition  points,  56;  of  measuring 
affinity,  36. 

ELECTROLYTIC  DISSOCIATION,  39. 

EMMEBLING,  92. 

EMULSIN,  84,92. 

ENZYMES,  84, 90. 

EQUILIBBIUM,  CHEMICAL,  37,  86. 

EYCKMAN,  81. 

FEBTILIZATION,  ABTIFICIAL,  80. 

FERRITE,  61. 

FORMULA,  STRUCTURAL,  4. 

GLASERITE,  118. 

GLUCOSE,  84,  86,  92. 

GOLDSCHMIDT,  47. 

GRAPHITE,  61,  66. 

GYPSUM,  100. 

HAMBURGER,  77. 

HARTSALZ,  121. 

HILL,  92. 

HYDROCYANIC  ACID.  84,  92. 

IONIZATION  :  and  physiology,  82 ;  theory 
of,  38. 

IRON:  transition  point  at  850%  62. 

KAINITE,  99. 

KALECZINSKY,  123. 

KEKUL£,  4. 

KIESERITE.  99, 100. 

KOEPPE,  79. 

KOHLRAUSCH,  41. 

LADENBURG,  3, 6. 

LANGBEINITE,  120, 121. 

LEMOINE,  91. 

LEONITE,  118. 

LOEB,  10,  74,  80. 

LOEWEITE,  120, 121. 

MAGNESIUM  CHLORIDE,  100, 105. 

MAGNESIUM  SULPHATE,  100, 105. 

MALTASE,  93. 


125 


126 


PHYSICAL  CHEMISTRY 


MALTOSE,  92. 

MAETENSITE,  61. 

MASSAET,  78. 

MAXIMUM  WOBK  :  principle  of,  31,  32,  35. 

MEYEBHOFFEB,  25,  97, 121. 

NEENST,  24,  41. 

OPTICALLY  ACTIVE  SUBSTANCES,  89. 

OSTWALD,  23, 41. 

OSMOTIC  PBESSUEE,  7, 74,  76 ;  in  bacteria, 
79;  in  blood  corpuscles,  77;  in  plants, 
76;  in  the  eye,  78;  measurement  of,  81. 

P£AN  DE  ST.  GILLES,  87. 

PEAELITE,  61, 64. 

PFEFFEB,  7. 

PHOSPHONIUM  CHLOBIDE,  33. 

PHYSICAL  CHEMISTEY  :  industrial  appli- 
cations of,  48 ;  introduces  new  concep- 
tions, 17 ;  is  not  merely  the  use  of  phy- 
sical instruments,  16;  its  founders,  23; 
its  place  in  the  science,  6 ;  its  three 
modes  of  application  in  inorganic 
chemistry,  24;  what  it  has  accom- 
plished, 6;  why  applied  chiefly  in  in- 
organic chemistry,  24. 

PHYSIOLOGICAL  CHEMISTBY,  9,  41. 
PLAN  OF  THE  LECTUEES,  15. 
POLYHALITE,  99,  100. 

POTASSIUM  CHLOBIDE,  99,  100,  102,  105; 
three  methods  of  obtaining  it  from 
carnallite,  48,  50. 

POTASSIUM  SULPHATE,  105. 
PBEDICTION  OF  BEACTIONS,  31, 33. 
EAOULT,  40,  81. 
REICHABDTITE,  118. 
REVERSIBLE  CYCLES,  21. 
EEVEBSIBLE  CHEMICAL  ACTIONS,  87. 


SALT  DEPOSITS  :  stratification  of,  99. 

SALTS:  deposition  of  three,  106;  depo- 
sition of  two,  102. 

SCHAUM,  53. 

SCHONITE,  100,  109. 

SCHWAB,  121. 

SEA  WATEB,  98, 101. 

SODIUM  CHLOEIDE,  98, 100, 102. 

SOLUTIONS,  SOLID,  59. 

STEEL,  58;  explanation  of  hardness  of, 
66;  graphic  representation  of  behavior 
of,  63;  methods  of  examining  structure 
of,  61 ;  tempering  of,  61. 

STEEEOCHEMISTEY,  5. 

SYLVITE,  99, 100, 102, 105. 

SYNGENITE,  114. 

TACHYDEITE,  123. 

TAETAEIC  ACID,  89. 

TEMPEBING  OF  STEEL,  61. 

THALLIUM  SULPHOCYANATE,  37 

THENAEDITE,  118. 

THEEMODYNAMICS,  20. 

THOMSON,  17,  31. 

TIN  DISEASE,  52. 

TIN:  gray,  52;  specific  weights  of  white 
and  gray,  55 ;  transition  point  of,  54. 

TBANSITION  TEMPEEATUEES,  in  alchemic 
change,  25. 

TEYPSIN,  92. 

USIGLIO,  99. 

VON  JUPTNEB,  58,  62. 

WlNKLEE,  6. 

WOBK  :  possibility  of  accomplishing,  as 

measure  of  chemical  affinity,  33,  36. 
YEAST,  84, 92. 
ZYMASE,  85. 


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